Try to repair avast… Have you tried the latest build? Build 1091???
Direct download links:
Free AV: http://files.avast.com/iavs5x/setup_av_free.exe Pro AV: http://files.avast.com/iavs5x/setup_av_pro.exe IS: http://files.avast.com/iavs5x/setup_ais.exe