Trying to remove other anti-virus and use only NAV

I have Norton Anti-virus and scan my computer regularly.  Today when I turned on my computer, the antivirus that I assume came with the computer, was running a scan and said I have 7 malicious programs that are all trojans.  I ran the Norton Anti-virus and it came up with nothing.  Sounds like a 'marketing ploy' because when I clicked to active the product, it was going to cost me $40. 

 

I have tried to remove the other anti-virus with no luck.  How can I turn the other scan off?  How can I get rid of it?  Any suggestions?

 

thanks,

boham

 

[edit: Changed subject for clarity.]

Message Edited by shannons on 07-13-2009 01:32 PM