My anti-virus scanner cannot detect viruses what should I do?  

I think you can do two things:

1.believe that your computer are not infected by any virus
2.change another anti-virus soft and scan again :)

I'm using Avira Anti-vir now, and I think it's doing a good job. Maybe you can try it.
Good luck :)

as i know virus have made for many many type and strong too, if you indicated your computer have a virus and already use powerful ant virus include norad avg or avast and still there maybe you need asistance to help.

Your antivirus might be not updated. Try to update and changed the scan settings on it; it might be just scanning a small portion of the HDD. You need to choose the "scan the whole computer option." You also might need to consider installing the newest antivirus on the market.