Sorry, but there’s nothing difficult about removing avast!. You just go to Control Panel / Add/Remove Programs and select avast! to be uninstalled. That’s it.

I don’t know what manual modifications you’ve done to registry etc… so it might not be possible anymore. Maybe the best you could do is to install avast! again and then uninstall it in the recommended way.
You may also try the uninstall utility - but I’m somehow worried that the changes you (or somebody else) have done may have done more harm than good.