Computer not Booting can hear fans die

[Tave504]

Cpu was crashing about 2 weeks ago. Brought it to the shop they said Ram was bad and installed new ram. When i plug it in at home it still wouldn't boot . The fans kick on and when it get pass the gateway screen it stalls and the fans die. It goes to a screen the says no boot files. I brought it back to the repair shop and they tested it and it worked fine (i watched him just plug it up) . Went back home same issue happened again. The repair shop wants to charge me 200 to come out and see whats going on. So i'm here to just get some opinions on what it could be. I have heard mostly that it could be the electrical wiring in my apartment. ( Around the same time this issue occurred i had a leak in my ceiling ) I've also heard that the it could be my power supply. I'm just trying to avoid spending 700 on a new unit or expensive repairs b4 window 7 releases.

 

[Tmagic650]

I would replace the computers power supply first. This would be the cheapest repair option

 

[Tave504]

i just spent 45 mins cleaning it out and that worked.... but i do appreciate the reply