Windows hangs at boot time

When I boot up after the computer has been off for several hours the computer will hang up at the Windows logo and the disk light will stay on. This does not happen every time I do a cold boot. I eventually have to press reset to get the system up and running. I have changed drives and the problem still happens occasionally. I am using a gigabyte board with the latest bios updates and have a AMD 64 3800 CPU. I have also changed out my memory which I am using 2 gigabytes. Any ideas what could be the culprit?