Norton Antivirus 2009 full-system scan?

I have Norton Anti-Virus 2009 (with Antispyware) and whenever I try to do a full system scan, it scans the same way as the quick scan. When it scans, it says "scanning commonly infected areas and start-up files." The full system scan only scans up to 6,000 files, but I can't change it to scan the whole system.  I've tried un-installing it completely twice and reinstalling it but that hasnt solved the problem.

 

How do i rectify this problem?