Before re-installing Windows 7 I suggest you try the following:
1) Click Start Orb -> type 'Cmd' -> right click Cmd and run as administrator -> type sfc/scannow -> wait a while till that has finished and then reboot -> see if problem solved.
2) Click Start Orb -> Control Panel -> Programs and Features on or off (top left side of screen) -> Uncheck Internet Explorer 8 -> Yes - Yes - reboot -> Click Start Orb -> Control Panel -> Programs and Features on or off (top left side of screen) -> Check Internet Explorer 8 -> Yes - Yes - reboot -> see if that has solved the problem.
3) If the above don't work then boot from your Windows 7 installation disk and select the top option 'Startup Repair' to see if that helps.
4) If none of the...