When I start my computer it gets to the post screen where it displays CPU and memory info, then freezes. Then the monitor goes off. The computer is still "on" as I can hear the fans and hard drives spinning. If I switch it off at the power supply and leave it a few hours it will boot ok. I've checked the disks for errors and there are none. I've checked the cards, plugs inside the machine are properly seated and they are. This happens around once a week, bearing in mind I boot the PC usually once a day.
Can someone give me an idea where to start troubleshooting this please.