PC freezes even at Dos prompt

Compaq Presario. PC will freeze intermittenly. Time Varies. It can be quickly or after an hour. Tried new power supply, new hard drive, removed all devices. Problem still appears. Disconnected hard drive, power and data cables, booted from a Floppy Disk. After a while the PC Froze again at the DOS Prompt with no activity going on. I’m now looking at installing another Mother Boards. Any clues.