take a look in your event log (event viewer) see if any programs are terminating abnormally, also before you shutdown check the task manager to see if there are additional tasks/processes you can kill off.
Do you run anti virus and firewall?
If you haven't been into CMOs then don't worry, The settings shouldn't have changed by themselves.
Disconnect any active peripherals like printer, flash drive, modem, scanner..
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"