It could be something to do with your internet options or you may have a virus.. it could be likely. To fix that just do the following steps..
1. Get into the Windows 2000 / XP Safe mode, as the computer is booting press and hold your "F8 Key" which should bring up the "Windows advanced Options Menu". Use your arrow keys to move to "Safe Mode w/ Networking" and press your Enter key.
http://www.computerhope.com/issues/chsafe.htm <----Only if you don't have Windows 2000/XP
2. http://onecare.live.com/site/en-us/default.htm <---- Free scan it removes anything harmful on your computer and puts it in quarantine or in otherwords stops the virus. The scan is a very deep and detailed scan from Microsoft, which is very secure.
3. Get http://www.malwarebytes.org/ <---- Free anti-malware which knocks out malware. If you have the boughten version then you will get, website blocking, automatic scans/updates when you want to, active protection, one lifetime low fee etc. Free version you have to do everything manually and you wont get some of the extra features.
4. I use Microsoft Security Essentials Anti-virus/Spyware & Malware. I never had a problem ever since I had all this with my computer. http://www.microsoft.com/security_essentials/
Otherwise try going here: http://support.microsoft.com/fixit/
If none of this seems to help then I reccomend you go to your local computer store for help or consult a computer technician.