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
(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.