Big troubles with my pro Avast

HI! Since I bought a pro version of AVAST in September 2011, actually before… (Had to buy it twice), I have had troubles with it. It simply stops working and I must uninstall it and reinstall it and it works another SHORT while. Then again I must uninstall and reinstall. It happens atleast every 3th or 4th week. AND now it isnt even one week ago since I did it last time. Now it doesnt work again. Is that what I payed for…twice?

Please help me. I have a good stationary PC with alot of Ram 64 bit win7. Nothing should stop it and it isnt even an old PC. I am really not very happy right now. I used to LUV my AVAST… I am loosing my faith here…

Which version…??
OS…?? (which SP)
Other security related software installed…??

Also what AV was installed before avast and how did you remove it ? did you use a removal tool to clean up leftovers ?