It could be something as small and simple as a fuse in the PSU. Any repair shop having a Volt-meter should be able to fix it.
The power went out all along our street for several hours last night. When the power came back on, I went to turn on my desktop computer.
Nothing happens. No sound, no lights, nothing. I've looked a little bit around the internet, and so have already tried: unplugging the computer, unplugging the surge protector, and plugging the computer into the wall instead of the surge protector. Everything else that is plugged into that surge protector (modem, monitor) works just fine.
For what it's worth, my computer is a Dell Precision 370--I don't know how old it is. I'm kind of at a loss, here.