Just a thought, as this was something silly and simple that caught me out with Avast!’s boot scan many moons ago. I don’t even know if it is the same now.

However, if I remember, when the boot scan finds a problem, it’ ask´s for a number key to be pressed (depending on what you want to do with the problem). I found that the ‘numeric keypad’ on the keyboard didn’t do anything and the scan would just sit there doing nothing.

Try (if you haven’t already) using the number keys above the alphabet keys.

It might also be an old problem that was fixed in version 4.1.389 (April 21 2004) that has crept in again.

Have a look here:-

http://www2.asw.cz/eng/av4_revision_history.html