My avast 5 was working fine until, I decided to try new avast 6 beta and right click scan wasn’t working (Its still beta I understand) so I switched back to Avast 5 and now right click scan is not working in avast 5 too I’ve tried reinstalling and updating but it is just not working. whenever I scan with right click nothing happens. now what to do?
I’ve had similar problems and this is what works for me - after installing Avast, even if doesn’t prompt you to restart, restart your computer and then try again the right-click scan. It should work.
Welcome to the forums, sonew 
In addition to zerotox’s suggestion, you might also try a repair of avast.
To do a repair of avast :
For XP -
Control panel > Add/remove programs > click once on avast to select it > click on Change/Remove > scroll down the left pane and click on repair > click OK > follow directions.
For W7 -
Control Panel > Programs > Programs and Features > click on avast > click on Uninstall/Change > click on Repair from the left pane > then follow the steps.
Yeah it worked thanks