A few weeks ago I had a lady bring in her new HP and her old, dead, giant desktop. She was obviously a heavy smoker, as EVERYTHING was covered in not just dust...but solid dirt. Like it was carpeted.

I switched her data to the new computer, she left me the dead thing, so I decided to take it upon myself to figure out what I can do to get it running, inexpensively.

After some major cleaning (2 bottles of contact cleaner and 2 bottles of canned air) I set off on my journey to find the problem. Turns out its the power supply.

A new supply powers it just fine, i mean, it takes a little time to boot up but it works. The supply that came with it I've opened. I replaced a cap that looked blown with the same specs on another cap laying around the shop. The old supply will still NOT work to the fullest. It powers on, but it does not power the board enough to display on the screen/even get to a post test.

I'd really like to complete the project of fixing this, but I'm assuming its a small part that isn't doing the job. Anyone have any ideas on what it could be?

All the other caps, resistors, and theres a chip; all look good. there is one fuse I'm looking at replacing cause the glass is kind of foggy like its blown but the PSU does power on. its 430W and the new PSU is 350 and works, so i dont believe the wattage is an issue.

Let me know if anyone has a clue/ran into this problem before and found the solution. (Yes, i know alot of you will probably post get a new PSU as a response......I'm trying to avoid that).

I have caps and resistors galore at my fingertips.

Replace the foggy fuse and report on what effect the change has.
One never knows!

you mentioned "one of the caps looked blown", look at all the other caps as well.
Any 'can' type capacitor that looks like it has a distorted shape, should be replaced. The electrolitic paste used in this particular type of capacitor starts to 'dry' out over a period of time, causeing the cap to lose its true capacitance, this can cause the power chips(mounted on the heat sinks) to give out power fluctuations, and could be the cause of some of your problems!