Avast Pro running on Windows 7 Proff machine has never found anything

I been using Avast Prof on a Windows 7 machine for the past 2-3 years. I scan the whole machine regularly but never finds any issues. Older version on this and older machines used to find issues. I think its just going thru the process and not really doing anything of value.

Has anyone any suggestions on how i can check the set up and know it is actually working per the design.

Gordon