This seems to match the problem you are having:

http://www.techimo.com/forum/t90467.html

Reboot when you finish following these instructions. I hope it helps and good luck.

EDIT: It appears that this specific case involved the Blaster worm. The symptoms you describe suggest a worm, as administrator accounts should be able to access this. Do you have a virus scan? Did you get this patch:

http://www.microsoft.com/technet/tre...n/MS03-026.asp

Also, what operating system are you running, if that does not fix it?

~ Traft