Desktop froze, now won't boot

I have a 5 yr old hp I have recently replaced the PSU and fans. Last month I ran diagnotistic on it and everything passed. However it has been for months with minor freeze ups. Then it froze up solid, restarted, got on the net and it froze again. Next time it showed an error message (no I don't remember it) and froze, last time was just the blue HP screen.
Now it is nothing all of the fans , lights, and usb attachments come on but nothing. I tried to put in a rescue disc, disc drive open and close but not spin. Tried a usb bootable, nothing.

any ideas what could have went out?