I'm sure IE8 comes pre-installed with Windows 7, have you tried
marsmimar suggestions?
Since, IE8 is a pre-installed program which cannot be removed, then have you tried using
SFC /SCANNOW Command - System File Checker, and then a
Repair Install if the System File Checker detects any problems.
Have you performed a full AV scan of your system?
Hope this helps,
Harry