My first experience with a machine going seriously wrong (as part of my pharm).

I find it not running. Press the ON button, nothing. Turn off the power on the power supply, turn it back on, press the ON button, the p/s fan jerks a tad. I've seen that before with a fried power supply. Get a new, slightly bigger one (350w instead of 250w), install, press ON button, the p/s fan starts slowly and spins but not full speed, the "power" led is not on but is sortof blinking and not brightly, as if it's not getting enough power to go all the way on.

So what next, swap a good cpu in to see if that's it? Or swap the cpu to another mobo to test it? Seems obvious enough, am I missing something?

BTW, this machine sat about 6 inches from the floor. I can see lint/dust in the heatsink fins, but can still see through the fins. It was my most reliable machine, up and crunching seti for 8 months straight, until the local electric utility gave me an hour outage that my ups couldn't take.