It could be the power supply, motherboard, RAM, hard drive, bad power switch, or possibly even the CPU. If it beeps, you might be able to look up the codes, but otherwise I'd either take it to the shop for repair or throw it away. Taking it to the shop is likely to cost you at least $150, so depending on how old it is, it might or might not be worth it. When we paid $2000 to $3000 for PCs, it was worth having them repaired, but nowadays it's more like TVs; when they crap out I often just replace them.
help me. long ago my computer died and wouldn't recieve power and i figured it was just dead, but i decided to take it apart to see if anything was wrong. the motherboard still lights up with power and if i plug the power cord in it still has power. No fans turn on and when i hit the power button nothing happens. Any tips? i've taken it apart checked everything and it's all in correctly the cord to the power button are hooked up correctly.