Studio XPS 435MT wont power on

I too am interested  in the root cause as I'm experiencing the exact issue with my xps 435mt which incidentally happened after a power outage.  I've just begun investigating myself.

Same happened to me last night after a power outage. exact same symptoms. I can change the PSU but of course want to know whats really going on here as you have fully diagnosed this and it did not sound like a simple PSU failure. What was the resolution?

I have the same problem.  After 15 to 20 attempts at pushing the power button it will usually come on.  I figured it was the switch itself, but haven't tried to replace it yet.

I have not resolved this problem yet.  I am not willing at this point to spend the money on diagnosing it further, but the issue still really bothers me because I feel I've checked virtually everything.  I'm still very interested in knowing if anyone else has any ideas, though!!!  

BRS, Im not sure whats going on as you have clearly done all the things I would have done. OK , I will speculate a little here so bear with me. Anyone else reading this please note these are wild theories. If we find something definitive I will post the solution.

Its not the PSU so no power issue. Did you unplug the accessories going into the MB to see if something else got fried? i.e. will it boot if other systems are not plugged in to the MB. I suppose this could explain the failure to power up even with a new MB, but I still dont understand why it would work even once if that was true.

Im stuck at the CMOS battery. Why would it work with a new MB ONCE, then exhibit the exact same symptoms... but clear if the CMOS memory is cleared?? 
Assumptions: PSU is good, Motherboard is functionally good as the problem still exists with a new MB of the same type, stuff plugged into the MB is OK as it wouldnt power at all otherwise. Fact: CMOS battery clears the problem but it recurs on second reboot. The only thing that has changed on the second attempt is configuration in the software/firmware somewhere different from the initial fresh settings (which is what you get when you take the battery out).

WARNING: Wild Speculation follows as I am not a computer or dell expert (but am an engineer so I like to diagnose things).... I wonder if the power outage caused some setting, perhaps in flash memory to get corrupted somehow. An overvoltage spike could do this to flash memory. Once it boots it reads the corrupted value and saves it to the CMOS memory and thus the fault condition persists. This would imply the corrupted value is not on the MB (or equally likely that I dont understand the way the BIOS load works or what it saves). Could you try reflashing the BIOS and see if this makes the reboot stable?

I'm thinking some setting in non volatile memory has been corrupted by the outage but have no idea what or where or how to reset it.  Any ideas appreciated and Ill keep thinking. Like you, I dont want to swap things out until I really understand what is going on.

Well, we had another power outage the other day and, of course, it would not power on.  Same twitches of the fans but nothing else.  So, as expected, I figured I'd take the CMOS battery out for a minute or two to reset whatever is getting screwed up and restart from there.  It worked before numerous times so I expected this would get me up and running for now.  This time, the lights on the PSU, motherboard, and power button flicker constantly (not blink - they flicker like high tempo disco lights or like a candle flame).  When I push the power button it again seems like it wants to power up but doesn't.  When I hold the power button, it sounds like I'm trying to start a flooded engine - the fans come on but only sputter as I hold the button - like they are working at the same pace as the flickering lights.  I AM STUMPED!!!!

I too am no cumputer expert and I've dignosed this so far by simple process of elimination and reading A LOT on the internet.  When originally diagnosing this, after the new motherboard was installed, and after getting the same problem, I did try to restart repeatedly by unplugging one component at a time to try and isolate something but that gave no results.

Keep the posts coming as I'm still ambitious in getting this resolved.  I don't know - maybe it's getting close to time to bring the thing into a shop :(

I too have a XPS 435MT with the same problems.  From all the posts on these boards and across the internet, it seems as if these systems are starting to drop like flies.

Since my system will power-on and boot after reseating the CMOS battery or clearing the CMOS via jumper on the motherboard, it would really appear that there isn't an issue with the power supply or other hardware/add-in cards.  I'm beginning to convince myself that it is something on the MB and I'm leaning towards aerobatic's speculation in the earlier post about something becoming corrupted in non-volatile memory and it is then loaded into the BIOS.  Thus explaining why it will power-on and boot the 1st time after replacing the CMOS battery or clearing the CMOS via jumper on the motherboard.

Extremely frustrating to say the least.  I hope someone figures this out.  I'm about to give up and just piece together a new system with a different MB.

I reseated the CMOS battery and lo and behold the system starts fine. Battery checked out OK as well which I expected. I am also stumped. I woudl assuem a new motherboard would come with a new and uncorrupted BIOS. Perhaps something on the other cards is amiss. I am going to reinstall the BIOS and see if that makes a difference and will report back when I cycle the power , but right now I want to just leave it running;-)

I still strongly feel this is firmware issue and not Hardware related. I suspect those people changing various boards and accessories have just acheived the same software/firmware reset. I sure wish someone from Dell would weigh in on this....

Hi brso9735,

I thought I would post my situation/results.  My 435mt was experiencing identical issues after I shut it down and unplugged it for the first time in months.  The only thing I could do to get the computer to turn on is the CMOS battery trick.  After several hours of internet digging, and inquiring with a friend who knows quite a bit about computers, we were both still a bit stumped.  That is, until I mentioned to him that the power supply that came with my system was only 300w.  The way he explained it (in layman's terms for me), the motherboard holds a charge, even when it is off.  The charge comes from the power supply and the battery.  If the battery was dead, and the motherboard wasn't being properly charged because of a weak/under-powered power supply, then the motherboard isn't able to do it's job at start-up.  So, he recommended that I get a better power supply of at least 500w.  I headed over to Microcenter and picked up a Corsair CX500 for around $63 (plus it includes an $8 rebate).  Came home, took out the two fans (and dusted them off while they were out), put in the new power supply, and everything is working perfectly again.  Crossing my fingers that it will last, but for now, my problem seems to be solved.  Not sure if this will help you, but it worked for me.  My friend was shocked that Dell would only put a 300w supply with the rest of this system.  He said it isn't even close to enough juice.

Best of luck.  Post back if you try this and it helps.      

rag47546...glad to hear that you have things up and running properly.

I figured I would post an update in follow up to your post.  It has now been almost two weeks since I upgraded the power supply, and my computer has been working flawlessly, with several shut downs and start ups just to test it out.  Actually, maybe even better than before.  I have noticed that it is running quieter, with a lot less fan noise.  My issue seems to be solved.  Best of luck to all.  

I have had the exact same problem for last couple months.  I have just been very careful not to turn it off, until my gf shut it off thinking it would save power.  I am not not a computer engineer, it professional etc.  I decided that since it ran fine, what PLAYU18 said about the power supply being under powered made sense.  I bought a 500W for about $45 and stuck it in.  I did not make any other changes other than some cleaning, and it powered right up.  I even tried my luck by turning it on and off a couple times.  The problems appears to be resolved. 

I have a suspicion that because these were early models with the icore chips, there might be an issue as they get older.  The cpu is more efficient in use, but powering up takes a bit more.  I had a black error screen that came up when i first turned on the computer for a while (I did not know what it was, but thought it was attributed to an upgrade from Vista to 7) which did not pop up with the new power supply.  NOTE:  I bought a new BIOS battery, but never took the old one out, I wanted to try just the power supply first.  Hope this helps.

This is very promising. More wild speculation follows... I still think there is a Firmware issue at the heart of this as thats the only thing that makes sense following a power outage which somehow can be 'corrected' by reseating the CMOS battery. What I suspect may be happening is that two systems are now powering on at the same time. The PSU cant handle the simultaneous drain and it shuts down (remember the film Apollo Thirteen when they tried to power the lunar module up in sequence). The new PSU has enough juice to handle both and it runs just fine even with a heavy load at start up. Once the system goes through the boot up stage I suspect the power decreases to some nominal level anyway.

Just a theory. It would explain why simply replacing the original PSU didnt make a difference as it couldnt provide enough power at start up.  I would really like to know whats at the heart of this but a new uprated PSU is certainly an adequate workaround.

Mine is still running as I havent powered it off so cant test the benefit of reloading the firmware for the BIOS, DVD and Video card. I did note that the Hard Drive has an uprated firmware available and the application note ominously cites a "hang up issue". I have not loaded new firmware for this but if I do I will report back.

This more for info at this point but very pleased to learn of a practical fix which also is consistent with my wild theories;-)

Could you post the model of the Cosair PSU you installed. This seems a solid fix from all reports.