when i right click on a folder, and tell avast to scan it nothing happens ???
it worked with avast 4.8, and i have restarted my pc which didnt help!
So are you not getting a results page displayed, see image ?
nope, im not getting that 
First try a repair of avast. Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button and scroll down to Repair, click next and follow.
What other security software do you have installed ?
Have (or did) you another Anti-Virus installed in this system, if so what was it and how did you get rid of it ?