XPS 8940, will not power on, green light stays on for 2 seconds but goes off - Nothing happening

we had a very quick power failure in our house and this unattended Desktop PC (a Dell XPS 8940 Desktop) no longer powers up.

My question is, is it the Power Unit (it's a 360 W Power Unit ... that is fried or could it also be the MoBo?

Yes, either or both. I suggest you have a local computer technician take a look at it (if not really to buy a new one yet).

Have you tried un-plugging from wall.

Press power-button a few times, then hold down for 15 seconds.

Let it rest for 30 seconds.

Plug back in and try to turn-on/boot-up.

And please, get yourself some dependable UPS-Battery units before the other one blows-up (like APC or CyberPower ... around 1000-1350 size).

@Tesla1856​ Thanks for responding. Will take the Desktop to a local service center working on Dell Desktop PC's. Quick question, when it comes to replacing the power unit, should I go for the 360 Watt unit (which is what is currently installed) or for the 500 Watt unit? It's not a cost factor ($70 for the 360 Watt vs $100 for the 500 Watt unit) but a question of will it fit?

What do you recommend. Other than this power problem, the PC has been working just fine. 

Wait to hear back. Thanks for the feedback so far (yes, absolutely, will replace the surge protector with a UPS Battery unit).

I suggest you stick to the Dell-OEM Power-Supplies originally offered for this model.

If it's been fine, I suppose another 360w PS would be OK. If you run a dedicated video-card in a PCIe slot (like Nvidia or AMD) ... there is really no reason to not go a little bigger (since you are replacing it anyway).

But like I said ... the failure could be anything inside and a XPS-8940 is now considered a Legacy model. 

@Tesla1856​ Thanks your quick response. Will stay with the same power unit as before (360 Watt) when I talk to the service center. Keep you posted but it may take some time before I know what needs to be done (Power unit only or both Power unit and MoBo). Thanks again.

Running a Self-Test on Your PSU without a Button

Turn off your computer.

Disconnect the power cable from the PSU and wait for 15 to 20 seconds.

After 15 to 20 seconds, reconnect the power cable to the computer.

The LED light should turn on for 3 seconds and then turn off.

If the BIST LED turns on, your power supply is delivering power to the computer.

If the BIST LED does not turn on or the PSU fan does not spin correctly, your power supply is not delivering power. Disconnect and reconnect the power cable and try again. If the LED still does not turn on, contact Dell Technical Support for repair options.

 I had something similar happen, and replacing the CMOS battery did the trick. 

@bradthetechnut​ Tried this step as well but no luck. Probably taking the Desktop to a service center for diagnostics and decide what to do after we get some input. Based on the comments from this board as well as the Dell Support Pages, it appears it could be a MoBo problem (maybe also the Power unit) and not sure if this expense makes sense. Have to wait and see what the estimate is.

@sabebbi​ If you try replacing the CMOS battery, remove the old one, then let the computer sit for 15 minutes before putting the new battery in and powering up. 

@strux​ I did wait for 15 minutes but this did not work either. Waiting to see what a service center says needs to be replaced. Bummer but it is what it is.

Here is the latest. I have decided to order a replacement power unit from Dell (same as original, 360 Watts). Hopefully, this will get this Dell Desktop PC back up. We'll see.  Most likely, if this does not work, I don't see any reason to continue to spend good money on other parts, like a MoBo (per Dell, there are 2 MoBo options, one for $190 and the other for $340 - unable to tell what the difference is between the 2, apart from the price). 

Have tried all the various suggestions mentioned by others. Thanks for the tips. 

@sabebbi​  Ebay has better deals on MB's if it comes to that.

Here is the latest. I got a replacement power unit from Dell and the new unit did exactly the same thing. Green light shows up for 2 or 3 seconds and then absolutely nothing. No fan, no nothing.

So, the new power unit is going back to Dell, hopefully, for a full refund and the PC will be retired. I could, of course, replace the MoBo only to find out that some/all of the other devices are also dead. So, it becomes a futile exercise. Not worth the hassle. Will be looking sometime soon for a replacement Desktop PC. 

Thanks to everybody for their suggestions/tips. Very much appreciated.

If you wanted, you could always take the PC to a computer shop whereas they can pinpoint and diagnose the problem which is difficult to do from here.

@bradthetechnut​ Understood but it will still come down to replacing a "this" or a" that" and it may or may not work. So, I will live with my existing Desktop PC, w/out having the extra Dell XPS 8940 available. Eventually, I will get a new one. Bummer. Will be more expensive but it will be a newer PC