Machan, may be you have enabled the option "delete pagefile at shutdown". if so it would take a long time to shutdown. Disable this option using tuneup system control or another way you prefer.
If you still got the same problemo it may be a stealth process (probably a virus). Open "Task Manager" & Stop all unsure & high resource using processes.
Surely this will free up your mind. @ last remember to run a complete scan by a trusted virus guard.
