Bad Processor ?

How can you tell when the processor is any good? Everything worked except I changed the memory and installed a new hard drive. Then The monitor doesn’t have a display, no keyboard lights, no beeps or sounds. No light on the A drive, the D drive light stays on, ejection doesn’t work. All IDE cables are connected properley, the jumpers are set to Cable Select. (Also tried M/S as well). But I hear and see the fans working. I don’t have much in the way of test equipment. Suggestions please? Thank you.