XPS 8940, will not turn on after power failure

What color is power button and is it steady or blinking? If it blinks, count the number and color of each blink.

Have you tried clearing BIOS?

1. Power off, unplug power cord from rear of PC
2. Press/hold power button for ~15 sec
3. Open case and remove motherboard battery (check Service Manual for details)
4. Press/hold power button for ~30 sec
5. Reinstall the battery (Time for a fresh CR2032 3-volt coin cell battery? ~$2)
6. Close up and connect only mouse, monitor and keyboard
7. Reboot

@Boo32 

" I have the system on a surge protector and battery backup"

Both or are they one unit? UPS's also are Surge Protector's and some have Surge Protector plugs only, not connected to the Battery Backup system. My CP1000PFCLCD from Cyberpower has 2 sets of power plug sockets like that. Still, unless the surge of power was severe, it should have worked.

"The monitor came on without a problem, but the CPU wouldn’t start."

Did you see the Dell Logo? Can you reach the BIOS (F2)?

Do you hear the fans starting or any other noise?

Can you use a Bootable CD or Flashdrive and look at the C: drive? Can find many on the web, or even the MS Media Creation Tool will allow you to reach a Command Prompt.

Does the power button stay lit?

When you power up the PC, and the

@Boo32  - Did you press/hold PC's power button for ~30 sec after removing battery, before installing new one?

Are all non-essential external devices disconnected (eg, power strips, surge protector/UPS, printers, scanner, speakers, etc)?

Other possibilities:

1. PSU is failing under load
   Disconnect all drives from PSU, except boot drive, remove all PCI-e cards, including video and WiFi. Reset BIOS again. Connect mouse and keyboard to rear USB2 ports, and connect monitor to onboard Intel Graphics video port. See if it boots now.
   
   
2. Motherboard failed
   Remove all RAM from motherboard, and reset BIOS again. Connect mouse, monitor, keyboard and power on. Listen for beeps (either 2 or 4) from inside the case.
   
   
3. Power button module failed
   You could replace the power button module, but no guarantees that's the fix.

BTW: Document date/time of power failure and resumption of power. Then contact your power company ASAP.  Since your neighborhood lost power, it's their fault. Ask what insurance protection coverage they have for customers in this situation. Document date/time/agent's name, and details of discussion when you call. Hopefully, they'll agree cover your costs to repair (or replace) this PC, without too much hassle.

Ron:

First, thank you for responding so quickly, and secondly sorry for the long delay of my response... I was suppose to get an email notification when someone posted a reply, but I never received anything.  I'm glad I just decided to check anyway.

The power button doesn't currently light up, so there's no color.  As I think I mentioned, when it shut itself down after the power outage, I noticed that although the CPU wasn't running, the power button was a steady green.  But again, when I couldn't get it to come out of sleep or hibernation or whatever state it was in, I did a hard shutdown by holding the button in for several seconds until the light went out.  Since then, nothing.

As for your battery suggestion. I wouldn't have thought the little bios battery would have stopped it from booting up, but I went ahead and removed it.  It was a little low at 2.95v, so I went ahead and put in a new one.  I reconnected everything.  When I plugged in the power cord, once again the little green LED came on for 3 seconds showing me the power source is working.  I push the power button and still nothing.  No lights, no fans, nothing.

So, if you have any other thoughts, this time I won't wait for an email notification, but check back here periodically.

Thanks.

Irv:

It is an APC single unit both surge and battery backup and both the monitor and the CPU were plugged into the side which has both backup and surge protection.

No, there was no Dell logo on the monitor when I came in.  Just a note saying "No Signal."

No fan running, just the green light on the power button.

Again, it acts as if there is no power, so I can't boot up with CD, flash drive or anything else.

Yes, did the 30 sec hold after battery was removed.  Matter of fact, I just did it again to make sure.  Still nothing.

Tried suggestion 1 and 2, but still no signs life.

 I know a bad power button is probably a long shot, but even though it is a bit tricky getting to its connection, it's probably the cheapest solution if it turns out to be the problem.  Do you know if Dell actually sells individual small parts like that?  If so, how do I locate where to do that?

I also appreciate your suggestion on the power company.  Unfortunately, it wasn't the power company but some outside contractor that was putting in cable or something and they cut an underground wire that cut the power to 10 homes in the area, and I was unlucky enough to be one of them.  If this becomes expensive, I can look into getting them to pay for it, but I'd probably have a hard time proving it was the power outage since it was on a battery backup.

Yes, I have a discrete graphics card, but again, there is no power going to anything, fans, drives, etc. Out of curiosity I did remove it and still nothing is powering up. 

As to the color of light on the power button when it shut down.  I may have been wrong and it might have been white.  Again I was quickly trying to get it shut down before the battery backup drained.  I saw the light was on (not blinking) and when I couldn't get it to respond, that's when I shut it down.  It hasn't shown any signs of life since... outside of the green LED on the power supply coming on for 3 seconds when I plug it in.

Speaking of which, my original thought was that maybe the power supply had gone bad, but unless the test Dell recommends where the LED that lights for 3 seconds tells you it's working, is wrong, it has to be something else.

As I mentioned, I saw in another discussion that some people with older versions of these models had occasional problems with bad power buttons, so maybe that's what it is and if I can find a replacement part, that should be relatively inexpensive repair. 

I'd think the Power Button could be checked quite easily? Open the case and follow the wires:

Should be quick way to rule that out? Just short the pins out at the motherboard... and then shut it down before removing the short but at the right time I guess? Might be 3 wires, one on, one the power, and one off?

I guess you could easily get the same answer with an Ohm meter between 2 wires and press the switch and see it it works?

@Boo32 -  Did you test the PSU as I suggested above by disconnecting/removing the surge/UPS, and all nonessential hardware from the PC? In your OP you said you disconnected and then reconnected everything with no success. But that's not the same as testing with all the nonessentials disconnected/removed.

XPS 8940 doesn't have a BIST test button, but this PSU can still be tested by following the BIST instructions for PCs without that test button.

Since there are no signs of life, I think that suggests the PSU failed, even if its LED is green on back of case. Remove motherboard battery press/hold power button for ~30 sec. Reinstall the battery then with case open, carefully plug PC directly into a working wall outlet. Now look for the LED on the motherboard.  If it's lit that means PSU is providing a small amount of power, but that's not enough to boot the PC. If the LED is off, either the PSU can't provide any power or the motherboard failed.

I'd contact that contractor immediately. The longer you wait, the more likely they'll deny that their blunder caused the problem.

Maybe it's time to take this PC to a reputable PC repair shop for testing and an estimate to repair it.

Yes, I did follow the BIST instructions for PCs without the test button.  It did exactly as they described. The LED turned on for 3 seconds then when out signifying that the PSU is working.

However, you mentioned the LED on the motherboard.  Prior to this, I never had this computer running while it was open, so I didn't notice if it had an LED on the motherboard or not.  I have an older XPS that has a tiny amber LED on the motherboard that is always on as long as the computer is plugged in, whether it's running or not. 

If you're saying my 8940 also has that little LED, well it's not on even when plugged in.  So, I'm now thinking that this has nothing to do with the power button, which I was wondering if it was bad.  So either the PSU is bad, even though the BIST test Dell describes says it's good, or there is a problem with the motherboard itself.  And if it is the motherboard, how in the world did a power failure, while on a surge protector with battery back up screw it up?  Even if the battery wasn't strong enough to keep it running for very long, I still don't see how it would damage it.

Unless you have any other thoughts, you may be right and all I can do at this point is take it in, see if they can diagnose the problem and see what it will cost to repair it.  Hopefully, it's not having to replace the motherboard, because at this point, I don't think I can afford to do that.  And frankly, on a computer that I only use occasionally and is only a little more than a year old, I shouldn't have to replace the motherboard already.

No, everything thing I've tried, I've plugged it directly into the wall outlet.

@Boo32 - Before you do anything, let me confirm the XPS 8940 motherboard actually has that LED, which I assume it has. I pinged my Dell contacts and will respond here as soon as I get a response.

Did you try connecting PC directly to a working wall outlet, without using the surge protector, UPS or power strips? 

Damage could have happened if the surge protector and/or UPS didn't react fast enough to protect the PC and/or if there was a surge larger than the surge protector could handle.

Did you see my post about bypassing the Power button? That would rule it out and point more towards the PSU?

Here's the answer : The XPS 8940 motherboard LED is next to the audio in/out ports.

It should be on all the time when the PC is plugged into a working outlet. If your LED isn't on, then suspect the PSU first, which is less expensive than a motherboard.

Keep in mind this is a customized PSU, so make sure any replacement you buy specifically says it works with the XPS 8940. The stock Dell XPS 8940 PSUs are 360W and 500W. If you have the 360W PSU now, go for the higher wattage.

This might be a DIY project. Watch this Dell video to see if it's something you can do without having to take it to a  PC shop.