Igor, I've tried Window Blinds and Icon Packager (the second is a buggy application) and they're not incompatible with avast.
Using WindowBlinds themes without problems with both avast Simple User Interface and Advanced Interface.
Well, maybe they're not incompatible, but we've seen quite a few conflicts in the past - and the symptoms were exactly the same (avast! splash staying in the list of tasks and the real scanner not opening).
So, I would suggest to disable those skinning tools first (and possibly also update to the latest versions of them, if possible) to see if it helps.