the first issue could have been the system overheated. on pc if a temp gets to hot it shut down to save itself. if there no video now and no beep codes. (more then one beep at power up). it could be the cpu or the power supply. but before we start replacing parts lets see if we can bring this unit back. i would open the case and if there a lot of dust blow it out and see if any of the fans are turning on. if there no fans could be a dead power unit. if you have some tech skills i would unplug power to the drives and remove the video card and see if the pc powers on. if you cant then i would look to see if someone had a spare one.
if the fans are moving but with no video card you dont get any beeps from the system board it could be the system board.