Unless its an unlucky coincidence, I was bit by the same problem. I saw a notice that there was a new version available, I didn't pay much attention and clicked through it. It installed the Pro version in trial mode. I decided to fix it later (go back to the free version).
The next day my computer just froze on the win 7 splash screen, using methods from sevenforums I was eventually get it to reboot several times, and thought everything was back to normal. The next night, it was back to the freezing condition. Again using methods from sevenforums I was able to restore win 7 to the day the avast pro version was installed, which I removed and re-installed the "free" version, and re-installed the windows security patches. I has been scanned in safe mode after I was able to get it partially back, but the first times it wouldn't boot into safe mode either.
The boot HD has been checked by 2 different status programs, and gets a clean report, I am still not sure the problem is fixed....
I have been using Avast for many years, this is the only time something strange like this has happened.
