Desktop icon not working after system restore

Hi all,
After updating to Mozilla Firefox 4.0, my computer started to act strange. I was receiving different types of errors and Mozilla Firefox kept crashing. To resolve this problem I did a system restore.
The system restore restored my computer to the previous day.
The problem is that now ,when I click on an icon on my desktop, I get the option to open the icon with the "Open With" dialog box.
I also tried opening icons via the Control Panel but I get an error which says:
"C:WINDOWSsystem32rundll32.exe application not found.
Could my computer be infected or did the Firefox installation corrupted my operating system. Is there a way to solve this problem without a clean installation?
Thank you friends.
