I'm working on a Dell Studio 540 desktop. Owner keeps it on constantly and after a recent power outage the unit does not power on. No fans, no beeps, no lights, noises ... Nothing.
So first thing I did was remove and re-install the CMOS battery. No good.
So next step I removed and tested the power supply with a multimeter. The psu tested okay. It was putting out the right voltages. I also shorted the power-on (green wire) to a ground and just had the hard drive connected and it powered the drive. However when I plugged the main 24pin to the motherboard it does nothing.
So one would think that there's a short on the MB? However I use a spare PSU on the the system. Plugged the everything in and voila! It turns on! Gets into windows no problem. I restarted the unit multiple times with the other PSU mulitple times just to be sure. All systems go. But when I change it back to the original PSU it's dead.
Now I'm confused. Does the MB have short or is the problem contained to the original PSU?
I don't have an issue replacing the PSU if that's the problem, but it may not be worth it if the motherboard needs to be replaced as well.
Also of note: one time plugging in the original PSU it blew my breaker. But it only happened once.
My guess would be that the PSU has a intermittent short but some else's opinion would be helpful.
If everything works on the motherboard when you test it with another PSU, it is most likely the PSU. Even if part of the PSU got shorted or damaged, it can cause it not to work like it does now.
That is why it is never recommended to plug a PC directly into a wall outlet since the circuit power can constantly vary depending on number of PCs using that circuit and surges/outages/sags. Using a surge protector or UPS battery backup can help protect a Pc.