Make sure you run all the latest updates from Microsoft. In Internet Explorer go to Tools-->Windows Update
You should be running some sort of antivirus if you're not already...McAfee ASaP is cheap and works well.
...you also might want to create a new user account in the control panel and then "User Accounts" make sure it is a "Computer Administrator". Try logging in with a different profile and see if that fixes it. There's a setting on your profile called the "Temp Directory" and if is directed to a folder on your computer which has been deleted or otherwise mucked up I think you could see problems like that. If my memory serves me there was a virus that caused a problem with right clicking but I'm not finding anything about that right now in my searches. Good luck.