This is what my friend wrote,i need help finding out what is wrong..I am thinking it is the power supply:

Moreover the computer crapped out, the hard drive doesnt get read anymore. i tried mixing the wires atht connect to the poer source, didn'twork. So I didn't bothher anymore. TheA drive don't work, the CD drive either, nor doe the Hard drive, the computer turns on, but nothign appears in the monitor.

reduce the system to minimum config. Motherboard, memory (if there is more than on piece try with only one (or two if they have to be paired) and try with different sticks), processor, video card (if there is not one on the motherboard), disconnect everything else but keyboard monitor and power from the back and inside and see what happens.

If it turns on and completes post, turn off and reconnect/install one device at a time until it won't. When if fails remove the last component and try again if it posts leave out the component and install another one.

if it still won't post give us the specs and then we can make futher suggestions.