Did your copy of NAV work correctly and malfunction or did it ever work correctly ?
Did you d/l your copy or did you install it from a CD ?
Are you sure that there were no error messages ?
When did you last d/l the virus defs ?
Are you able to log on to the Symantec website ?

BTW, I'm running NAV 2003 on a Win XP Pro machine.
I've d/l all the LiveUpdates w/ no problem.

If the uninstall/reinstall solution doesn't work, you might think
about (a) insufficient system resources or (b) a virus/trojan that disabled your copy of NAV.

Just my $.02 worth.