Smart Scan crashed a Vista CPU

Free Avast has worked well. A recent “free” update included an option called Smart Scan. I had never seen this loaded before. I let it run and it seemed to perform well. Then, I made the mistake of letting it “Resolve All”. Not being familiar with this new option on my Atom based Vista laptop, I let it finish and then Restart. The restart was very odd; took about 10 min’s. Afterwards, some programs took very long times to load and run. Others just plain would not run. Even Windows Update would not run. I tried a Restore and that did not work. The computer was a mess. It acted like the Registry was all screwed up and some settings changed.
Have spent $$ and countless hours trying to get the laptop working again. It is semi-revived however, it will not run as before and programs are still slow to run, as if there is a long hunt in the registry for proper links. . . . I have used the usual methods to clean up and organize the registry and this helped “some”. Very frustrated that Avast loaded this Smart Scan on my system without telling me about it and giving me a choise to NOT use it… .

Vista with what SP ?
What exact version of avast ?
Is there any other security (related) software installed ? (or was there)

The smart scan has been in avast for quiet some time and only runs when the user tells it to do so.
It also can run right after installing avast, but it will tell the user that it will do so.