The PSU is complex and generally doesn't completely fail, so seeing the light on the motherboard doesn't indicate the PSU is good, only that the standby power is being supplied.

Personally, the first thing I would try is a new PSU.  Actually, I would try stripping the machine down to the bare minimum first.

Is the CPU fan working?

Peter

I would strip it down to just PSU, motherboard and front panel switch.  It should beep to complain there is no memory.  If it still switches off, then it looks like either PSU or motherboard (or possibly the front panel switch or CPU, but these are less likely).

I don't have this model, but you can search these forums.  I believe there have been some common problems with this model, but I don't think this is typical.

By CPU fan, I meant the fan the cools the CPU (what you call the case fan).

A BIOS problem could conceivably cause this problem, but if it is, you can't fix it.  The only thing you can do is reset the CMOS which is worth a try.

OS: No, you aren't getting to the point of passing control to the OS from what I understood you said.  It doesn't sound like you ever get to the Dell BIOS screen.

HD: Not likely unless it is causing the PSU to shutdown.  That's why I would try disconnecting it as part of "stripping it down"

Peter

Thanks for the reply,

What do you mean stripping down the machine to the bare minimum. Just 1 stick of RAM and the hard drive connected?

There doesn't seem to be a CPU fan on this unit. It has one of those air tunnel chambers over the CPU heatsink and the case fan is blowing into the tunnel and over the heat sink.

 I have a couple of 20 pin power supply's laying around but no 20+4 with SATA power unfortunately.  I guess I'll have to buy one just to test it :(

I just wanted to be sure this wasn't a common issue with this model.... Possibly linking back to something more of a pain like the MOBO or a OEM switch board on the case or something.

BIOS maybe?

Is there any chance the OS or the hard drive is to blame? If so I would have seen an error or BSOD before shutdown right?

Thanks again,

-Alex

Ok hopefully i'm getting to this before you've wasted too much time on this.  I've had this problem for months and after doing several things to get to the bottom of it (swapped out RAM, installed a new 500w Power supply, checked core temps, scoured the net for advice, and finally had a IT professional look at it) it comes down to there's a problem with the mother board.  I have the exact same system and the exact same problems.  Some days the system is in a good mood and i can get it running for 20 minutes to even an hour if i'm lucky but suddenly w/ out warning *pop* it's off and cycling again like you described in your first post.

I'm trying to decide if i blow the $ and get a new system, order a new mobo from dell, or go searching on ebay.  System is only 3-4 years old and the issue has really soured me on Dell.

1. Unplug the power cable from the back of the computer.
2. Push and hold the power button for 5 seconds to discharge residual power.
3. Remove the computer cover.
4. Strip the computer down to only the motherboard, processor, power supply, and control panel switch. This includes removing the power cables from any hard disk drive, floppy drive, or optical drive.

after that: Check the Status of the Numbered Diagnostic LEDs by first: 

1. Unplug the power cable from the computer.

    

2. Press and hold the power button for at least 5 seconds to drain any remaining power.

    

3. Disconnect all devices from the front and back of the computer. This includes the keyboard, mouse, monitor, speakers, printer, and any network cables.

    

4. Reconnect the power cable to the back of the computer.

    

5. Press the power button and watch the LEDs on the front or back of the computer.

    

6. Read the lighted diagnostic LEDs on the back of the computer.

Pls. reply if the diagnostic lights changed or not...
 

OK I removed all the RAM, disconnected optical drive and hard drive, removed NIC and video card.

It's just down to Power supply, MOBO, switch on front.

I plug in the power cable to the P/S and it turns itself on.....

I get a few long low beeps.... "Memory not installed I assume"

I see the MOBO light is on steady green.

And the front is now showing only the number 1 LED illuminated.

It's been about 20min. and no power down yet....

Could it possibly take longer to glitch out because the draw on the power supply is so low with nothing else connected?

Actually, is it possible that a test like this will not diagnosis a faulty power supply because the load on the power supply is not as heavy as it is with multiple components connected. Therefore its not getting hot enough for a thermal shutdown of there is not enough current traveling though the faulty component to make it auto shut down?

I've been battling this for a while now and I can't afford to go out and buy a Power Supply if it's not the problem.

Thanks for all the input everyone I really appreciate the help!

Yes, you are right.  This is not a definitive test.  But it does show that the machine behaves normally under those conditions.  I would add the memory back and then the video card (presuming it is ok with the memory back in).  If you get video and no shutdown, I would keep adding components back until either the machine works or you get back to the failure.

Yes, it could be the PSU and it only fails under higher load.  A known good PSU could determine if that is the issue.  That is one of the first things I would try.

Peter

UPDATE !

I just went and checked on the PC and it was beeping and turning itself on and off.....

Looks like I just had to wait a few more minutes for it to manifest itself again.

Prob. the lower current draw due to all the components being disconnected.

Looks like I'm off to buy a new power supply : )

I think I'll also add another case fan to help dissipate some extra heat off the new power supply.

I'll post up tonight with the results

Thanks again !

Just a note on the PSU and the case fan.  The power dissipated in your system is determined by the components powered by the PSU, not the PSU itself.  A PSU with a higher wattage rating only means that it can supply more power if needed, but the power needed is determined by everything else (e.g. you might upgrade the PSU if you change the CPU or graphics card to something that consumes much more power ). 

The heat generated by the PSU itself is a function of the power supplied by the PSU to the system and the efficiency of the PSU.  So if the PSU is low efficiency, then it will generate more heat.  Hence, changing the efficiency of the PSU is all that matters for heat purposes, not the maximum power rating.  Of course, the PSU fan tends to blow the PSU heat right out the back anyway.

Given your symptoms, it sure sounds like something is overheating.   If the cycle time is longer than before, that would also point to the PSU, because with the lower load, it should take longer for it to heat up to the problem point.

Peter

Grrrrrrrrrrrrrrrrrrrrrrr : (

I went out and bought a new power supply a nice 500W Antec,

I came home and installed it. Powered right up.....

Lasted 10 min. now it's back to powering on and off on it's own again....

No beeps, no warning, no on screen messages, I'm going crazy here...

I just wasted 70.00 and 2 hrs. in the car for a part I didn't need.

What a bummer

That's too bad.  It is hard to determine the problem with the symptoms you have.  That's why it is good to have a spare PSU around for debugging situations like this.

There are stories of problems in which Dell replaces the motherboard, the PSU and other components and the problem is still there.

In your case, what's left is:

1. The motherboard.  This seems to be the most likely suspect now.

2. The front panel/switch.  I wouldn't expect that to be the problem.

3. The CPU and CPU cooling.    CPU's seem to fail very infrequently.

Peter

I have an E510.  Most of the E510/5150 model (the 5150 is identical to the E510) problems over the last two years have been either power supply (about 90% power supply) or motherboard.  There has been an occasional front panel but in your case I doubt that it's the front panel. 

First thng I would do is clean off the old CPU heat sink compound and reapply new compound and see if that changes anything.  Since you replaced the power supply and it ran for about 10 minutes before having problems again could remotely be associated with CPU overheating.  The CPU has built in thermal protection and will power the PC off if it gets too hot. A tube of heat sink compound is relatively cheap and one fairly easy thing to do before going for a new motherboard. 

If you go for a replacement motherboard, only another E510/5150 motherboard will fit and work.  I don't think there are any new boards remaining so you will have to look for a used/refurbished board.  Do a google search as there are companies that sell E510/5150 motherboards (last I saw the price was in the 100 to 125 range).  There were several part number motherboards used in this model, the 0HJ054 was the last one used. 

Although you replaced the power supply and it didn't fix the problem it wasn't really a waste.  We have many (hundreds) of documented cases of E510 power supplies that have failed.  Also, depending on how a power supply fails it can also zap the motherboard.

i'm having the same issue.  the problem is the actual button/switch itself.  

1 - the button on the front panel actually pushes a plastic lever inside which taps the real power button.  take off the from drive panel cover and you will see the clear plastic lever.  CAREFULLY put something between the lever and the actual computer frame - do NOT break the plastic lever.  try a small screwdriver that you can leave in place just to prevent the plastic lever from touch the actual switch.  then try turning on the computer by pushing the small black button on the switch inside the frame.  use a plastic straw or something that wont damage the inside - it needs a very light touch.

2 - if you want, remove the actual plastic lever and use your finger to turn the computer on and off using the real switch.  the spring in the switch might be sticky which is why it keeps cycling on and off. try cleaning it out with air or even your finger.

if that works for you, just replace the inside switch.  Dell told me it's about $75, but im going to look for it elsewhere.

here's what mine looks like right now jury-rigged.

I agree with janbel1017.  The computer ran for hours with the PCB unplugged.  The PCB has the power switch, 2 USB jacks, and 2 audio jacks.  Dell will call me back with a price for the PCB (maybe), but I wonder if the replacement part will have the same defect.  I took the PCB out and cleaned it and banged on it.  In WinXP I used Control Panel, Power Options, Advanced, to set the power button to "Do Nothing".  We'll see if this is end of this problem.

Too bad Dell wouldn't admit to anything -- no recall, no available part or pricing, no help at all.