If you search the forum for 'RPC' you will find a lot of threads about this...
Probably, you just have to check if the two avast! services are running and set to 'automatically start with windows' (Administrative Tools > Services ... right click the services and choose Properties).
Of course, I suppose the RPC service is running or you won't be at Windows
![Grin ;D](https://forum.avast.com/Smileys/default/grin.gif)
(Remote Procedure Call is needed by avast!).
Sometimes, just booting solve the problem.
Others, you may uninstall, boot, install and boot again.
Wellcome to forums.
![Wink ;)](https://forum.avast.com/Smileys/default/wink.gif)