If you've just installed AVG Free edition there is the facility to make a "Rescue Disk" that you might not be aware of - Just click "Service" from the top Menu line then click "Rescue Disk" and follow the instructions.
I managed to get my PC infected with a virus which AVG detected on Boot Up but couldn't heal at that point, so prevented the PC from booting any further into Windows.
The rescue disk can be used to Boot-Up the PC and run the AVG program without Windows loading - in my case AVG was then able to remove the virus wihtout further problems allowing me to restart the PC as normal.
Coconutty
