About a week ago my computer started randomly crashing and I would have to turn it on and off about 5 times before it would start up again. Now I can't turn it on at all... I switch it on and the fans turn on but nothing comes up on the screen. I think that the reason it was crashing was because of overheating. I changed my motherboard a few months ago but didn't change the thermal pad on the p4 (didn't know it was necessary till now). I've now taken off the thermal pad and used some thermal grease but it still won't turn on. I've also tried a different graphics card and power supply but neither helped. Is it possible I've damaged my cpu? I thought that it was pretty hard to damage a p4 but I am not sure what else would cause my computer to stop working

u prob fried ur p4 but try to reset your cmos by movingthe jumper on ur mb

You're right ... it is pretty hard to damage a P4 (though not impossible). When you replaced the CPU did you (1) clean off all the remains of the original thermal pad, and (2) apply a thin application of new thermal grease? Too thick a layer of grease may also hinder your cooling. [BTW, did you also connect the auxiliary 4-pin power connector to the socket on the m/b next to your CPU? I forgot to connect that on my PC one time, and it wouldn't boot up at all.]