right clicking on desktop locks system

actually it gives me an eternal hourglass

other apps will still work but Windows stuff won't work, like I can't even open the Start menu when I have the hourglass

but if I reboot I can access the Start menu just fine until I right click the desktop and get the hourglass

I ran a virus scan and it showed changes to the MBR, boot sector and shell32.dll

I already ran fdisk /mbr with no changes

any ideas?

should I replace the dll? can I just paste a new one in there and reboot or will it have to be registered?

could my hard drive be compromised?

whats up with the changes?