Are you running NPE because you feel you have been infected? If so, it is possible you hav picked up something that is able to disable your scans.
I would suggest you sign up at one of the free Malware Removal sites below. Do not try to do anything on your own as it could make things harder for the Malware Removal expert at that site to help you. Choose one and stay there until your system is clean.
http://www.bleepingcomputer.com/
http://www.geekstogo.com/forum/
http://www.cybertechhelp.com/forums/
http://forums.whatthetech.com/