Turn the computer off,open the case and have a look at the power cables going to the motherboard.They are different to the ones going to hard drive and floppy drives and so on. You may need the motherboard diagram to help find the correct pins to plug them into .If they are already connected ,make sure they are on firmly ,but dont push to hard ,just enough to make sure there on right.
If that solves the problem then great if not ,you can try checking the mode your bios is swicthed to ,like raid ,native etc.If thats all good,make sure the fans are working ,there are usually 2 of them one on top off the cpu and one in the power supply area make sure they are turning,Cause if they dont spin ,your pc dont run.
Thats all i can say on this matter.
jim
April 2006