System does not shut down.. Norton auto-protect detects trojan and other attack but is blocking them?

System does not shut down.. Norton auto-protect detects trojan and other attack but is blocking them... Since these attacks have started my system does not shut down as it normally should. I have to switch off the mains to shut it down... found some autorun.inf files deleted them... Also Norton is not running fine where scanning is concerned. If i put it to scan it keeps scanning indefinitely does not stop even after 2-3 hours...