Hi Patrick, thanks for the quick answer.
Yesterday i tried to do what you suggest, i removed avast and i tried to install microsoft security essentials (MSE).
Uninstall worked fine, but while installing MSE system freezed, so i had to restart pc. On following try the application do not install because of an error.
The problem is that the system is still instable, nothing has changed. I'm answering today from my work place, because yesterday from my instable pc, i tried several time but never finished because of continuos BSOD.
I' ve to explain better one thing: I talked about an upgrade from Wxp to W7, but actually i did a brand new installation not an upgrade. So, avast was the last version downloaded from avast site.
Have you any more suggestions? do you think is better to do a new "Windows7_Vista_jcgriff2.zip"?
thanks in advance
Andrea