If you haven't run any scans try running your anti virus and AVG ANTI SPYWARE in SAFE MODE
Regarding the active desktop issue,check this LINK
Since the computer is shutting down I would run some scans.
Someone PLEASE help!!
My computer keeps giving me this error: "Active desktop has been turned off. To restore the active desktop, use the following troubleshooting tips." I am operating on Windows 2000 and everytime I click on "my computer", "desktop", or anything associated with the desktop my computer with shutdown and restart by itself and then give me the above error. I have tried all the troubleshooting tips it provided yet nothing works!