What hally says about showing hidden files and folders it's true, i know because i use win 7 64 bits, and like other windows versions, if u want to see some application data, you need to unhidde it, because it gets protected by the OS. And i have used a registry cleaner for avast, because sometimes, it forget to delete some keys. Now i dont have a record of everytime i do a registry clean. But i assure you "sometimes" avast uninstaller, not aswclear, left some registry info in the OS. And rarelly ocations, some files. But with aswclear, nothing is missed, because it fully delete all avast info from the system.
Just download avast clean tool aswclear from the forum, and run it in safe mode, it will delete all avast info, and then after a reboot, you can proceed to a "fresh" install of Avast 5 in the version you want.
( Note: You will need to Show.. Hidden Files & Folders )