Hold both mouse buttons when you turn it on or reboot and see if you get the early startup boot menu. If you do, then your problem is minor. Make sure the ribbon cables going to the I/O board are not misaligned by a pin. You may need a flashlight to see. Try a different power supply. It's just a standard AT power supply and it's easy to swap. I just swapped mine out and it solved random crashes and periodic reboots I was having.