my pc, also slows down when i try to install avast 5 pro. And the worst part is that i cant stop the shields , and i need to uninstall it. So the only way i can use avast 5 is with the free version and my pro key. Also i lost the internet connection. And i have done more than 8 boots and everything keeps the same, my pc not responding. Also i have created a record of my problems during setup, but nobody have answered my problem. So i will stick to v5 FREE, because is the only way i can use v5 of avast antivirus.