I have an HP Pavilion a522n with Windows XP
My fiance decided it was time to open the computer case and dust out the inside.
Now the computer will not turn on at all. When I plug in the computer to the outlet, the lights that show it has power, flash on and off very fast. But the fans do not kick on and the Power button does not work. Not even the disk drives will eject. So I know it must be a power issue. Also, when I unplug the power cord from the computer, the power light still continues to flash for about a minute until it slowly stops.

Could it be the Power supply or the motherboard?
When the computer was cleaned, do you think something shorted out?

When I talked to Customer Support over the phone, the guy had me unplug everything and plug it back in, and make sure no wires were damaged. I found nothing wrong.

Has anyone heard of this before?

Have you checked the powersupply switch? My wife made that mistake once. she called me at work: HEY THE PUTER WONT TURN ON.. She just accidently flipped the PSU switch witch cuts power to the whole system..

IF that isnt it (Which it probably wont be) there are some things to check on the inside...
There are a couple of plugs that go from the Switch to the Mobo. Trace those down and make sure they are connected properly.. If you are still having troubles after that post back...