My friend has a pc, that wasn't cleaned in a loooongtime, so we took it a part and cleaned it out properly and stuff, i checked to see if there was any corrosion on the board due to the dust and moisture and i found none. After putting the system back together, i turned it on,it booted up fine and all, so i turned it off to add in the other hard drives, after adding the hard drives i tried to turn on the computer, but it would not turn on any at all (the motherboard has NO standby light), i jump started the psu after fully disconnecting everything and it worked fine, i hooked up a fan to it and it worked also, connecting it to the board i tried turning it on again but it still wouldn't turn on. I pull everything out of the case and hooked it up, it turned on again. so i turned it off after awhile, then placed everything bk in the case, this time it didn't turn on, so i checked the wires and all still no boot. I moved around the wires and let left it for a bit and tried turning it on again, this time it came on. i turned it off again and now it won't cum on again. any ideas what maybe wrong? I am thinking the power supply maybe bad.
I didn't understand much of that but it sounds like you are having intermittent power issues. Get a power supply tester or take the power supply to a local computer repair shop and ask if they will test it. Most likely its the power supply, if it was the motherboard it wouldn't be so intermittent.
Cheap power supplies are very risky to use in a computer, there are a couple decent cheap brands, but even they cost considerably more than the cheap crappy brands people often buy. You should avoid those at all costs, because they don't last, often cause instability issues due to non-stable voltages and currents, and put the rest of you computer at risk. The issue you face with the computer is the faulty PSU may have in fact stuffed the rest of the computer, or at least the motherboard. If you do need a new power supply, get one thats decent enough that you can reuse it in a new computer build