video/boot troubles

I am having trouble finding the problem on my pc. It started out having trouble turning on. I would have to restart it many times before it would finally boot. Then I would leave it on because the problem was getting worse. Now I can not get any video and it doesn’t sound like it is going through the boot process. I have changed monitors, video cards and power supplies. So far I am getting no where. Could it be the hard drive. I never had any error messages or chkdsk screens. Anyone have any thoughts.