Do u received any msg when the pc is shutting down?
Can u giv me specific about ur pc spec like OS? speed? ram size?
Also what program that cause ur pc shutdown except IE?
After the pc shutdown will it restart again?
Are you shure that this is a shutdown? It can be that there is a BSOD, and system automatically restarts after a crash. Under under your windows install directory there is a subdirectory called minidump. Do you see any files there?