ya ....
i too agree with ashu....
first of all run a good registry cleaning software like tuneup registry cleaner or registry mechanic of PC tools software......
or if u know when the problem was actually started ... then if possible try to restore to the previous (b4 problem was started) ..... as restoring will will bring back the registry settings...
otherwise try reinstalling NAV and then clean uninstall ....
and persionally i suggest u to use avast antivirus which is the best i had ever seen .....