It sounds like you have a corrupted user profile, or maybe even malware. To start with, I would open the Control Panel, then the User Accounts and create a new user with admin rights. Once there, test to see if the problem continues. If not, the it's possible only the previous user profile is bad. Still, it would be good to check for malware, just to be sure. As such, click on the link below and follow all of the steps/scans to the letter, in the order given. It will take a while to run all the scans but it's worth the effort.

“Expand” the post titled: "Please try this" at the link below:
http://www.cnet.com/forums/post/f742c795-5881-433b-a29b-6d758efe5cd3/

If everything comes up clean, the you know it's only a bad user profile and can simply copy all your files from the previous user account to the new one, then delete the old account.

Hope this helps.

Grif