Power unit fan makes noise - Switch off and attempt to clean fan - reinstall, computer works OK - Slight burning smell - switch off - buy new power unit and install - Switch on, computer works fine - 30min later, computer switches itself off - burning smell again. When I powered up, the power light on the tower unit continually flashes and the monitor displays NO SIGNAL. I have checked the video card and seems to be seated correctly in the motherboard. Have I damaged the motherboard or has the video card been damaged?
Once you've fitted a new PSU - if things still don't work, have you got a spare graphics card and/or memory module you can try? At least you then do a process of elimination, just in case the motherboard or anything else has been damaged.
Incidentally, a faulty power supply (regulator duff) blew up everything (bar CPU) in one of my computers.