I'm running an MSI micro-atx mobo, and a Seagate 320gb SATAII HD. In most cases the computer and BIOS will see the HD with no problems, however, every once in a while it will no longer see the HD after a power down or restart. When I open the case I hear the HD spinning so it has power. Right now the fix is to unplug the SATA connection and the power connection, and plug it back in. After that it will see the HD again for a few more times. What could be the prob in this case?

To rule out a hardware issue, try to run the diagnostic utility to see if anything is detected.

http://www.seagate.com/support/disc/utils.html

Let us know,