Can you do a system restore to before you removed AVG?
Do an online AV scan, such as from click here
Then remove AVG again; reboot and clean the registry.
Then install avast from click here and choose the regular install option.
After a reboot it should appear in the right hand corner of the screen (system tray)
I update Avast by clicking on the icon in the system tray and choosing update.
It will scan emails as they come along.