That's usually the sign that one or both are toast. You can follow the usual DEAD PC PROTOCOL and strip it down but that's your choice.
friends PC, eMachines w1640, winXP ,athlon 1600+, 128 ram. heres the problem, initially he said the mouse froze then the screen went to black. did a restart same thing. brought it to me. i took cover off, grounded myself, blew some dust out of it, hooked my monitor to it, and as soon as i plugged the power cable in on the back, the cpu fan started running and no boot up. there were no beeps, just the fan. the hard drive wasn't running either. the power button on front will not shut it down and the light was not on.