MY friend have a desktop computer and I think it's working fine. But The problem is when you turned it off after using and tried to turn on again, there is no power, you can't turn on. you must wait for 10-15minutes to turn it on. What is the problem why we cant turn on immediately after shutting down. Do you think the problem is the power supply? His motherboard is ASRock G31M-VS2 and running with OS windows XP. the power supply is only 285 watts.
The PSU is dead or almost dead! It sound like the 10-15 minutes you have to wait is for the power to be completely drained from the PSU before it can work again. If that's the case then parts inside the PSU are probably damaged or have reached the end of their life.