My friend just brought me his XP computer today. He installed AVG 8.0 last night, and his computer got stuck on Compaq logo screen. I tried to help him last night over the phone, but he's not to computer savvy, and nothing worked.
Finally, I was able to get to Safe Mode, and uninstall it from there.
I restarted in Normal Mode, but the computer was very slow. Surely enough there was a bunch of registry leftovers.
It toook me some time to trace all of them.
Installed 7.5, and things are back to normal.