I have avg antivirus on my computer but my computer can't see it wuy
I have tride to dounlode a new antivirus but it still says I do not have any anti virus programs on my computer.

I'm assuming Windows 7 here.
Simple open the action Centre and click the link that says NOT to monitor your AV solution as you have one installed.

The Action centre can get "confused"

Sorry I have windows vista

In Vista I believe it is called Security Center. If you have one installed and are utilizing it properlly then I wuldn't worry too much what Windows keeps telling you. Their prompts for AV's are sketchy (at best)