There are two things I would look at. One is the memory. It is possible that once the system heats up, there is an area on the memory chip that is bad. This is often the case when you get the "Blue Screen of Death". Replace all the memory. The second thing I would look at is the CMOS battery it could be starting to go out. Make sure that you also have the latest BIOS update for your motherboard. There is one other option but it is really hard to tell. It is possible that the hard drive is going out. I don't mean with a crash or anything but it has been known for the spindles to wear and the hard drive disk spins slower and slower. So since it is not spinning at the speed the motherboard expects, the motherboard starts acting up. Hope this helps. Cindy