From my side, here are some observations/info on this 'problem':
Info: The PC is a P4 with 1GB DDR RAM. Two IDEs connected to two Western Digital hard disks. Another two IDEs were connected to Samsung DVD ROM and TDK CDRW. Oddly, only one of the two CD/DVD drives can be detected by Windows. I removed the IDE from TDK CDRW so that I can use the Samsung DVD ROM to play movies. The movies were often found sluggish and stuttering, and worse, resulted in auto-restart.
My step: I disconnected both the IDEs for Samsung DVD ROM and TDK CDRW. So the PC IDEs are only connected to the two HDDs. Auto-restart still occurs.