It sounds to me like something is not right. If you are using PCGuard ensure that you have updated it to the latest Virus definitions, and then if you can undertake a full system scan, should be option to do this in the software. Never used PC Guard, but it should be like all other Virus software.
Once you have undertaken a scan with the latest updates installed, if you have a virus this should pick it up.
Ensure it is always kept upto date.
I would also recommend installing other Spyware software, should as SPYBot (Search Google), which is also useful to run along side your virus software.
Also have you got a firewall. (Software or hardware). Zonealarm is a good choice for the amateur user (again search google).
Best of luck.