I think my little problem with the mouse started when i have first installed avast 5 (I was running avast 4.8 before). I don't know really when it was but more than a month ago.
The problem of Avast stopping, I don't really know, I noticed it first about two weeks before starting this topic. I don't remember if I already had MSE or if I installed it later.
(I've already uninstalled MSE, following your advice)