Help MY Anti virus freezes when it scanning

Hi guys
Can you help Me out here been running your antivirus scan today and it started to freeze up on me
i read your post about it but call me stupid bol
but what is DEP and how do I go about finding it im just a novice here
meny thanks
it seem to be stuck on a crucial drive system32/drivers/pfc.syc
it wont turn off either which is annoying the way to shut it down is to reboot it
have you got any suggestion
meny thanks