vista freeze's during scan

Im heloing a friend out and she has vista on her desktop. It wasnt connecting to the internet after her teenage son went on line and downloaded a few movies.

I got comodo installed, i had to manuelly update the virus def file.

when I do a scan the computer always freeze’s in C: // windows/system32
its mainly freezing on windows media player files.

I can do a manuel scan and add everything but the system32 fil and it runs good. when i do a system 32 scan it freeze’s

Any suggestions?