Nice start... Yes, and you won't get anywere with attitude like that. Never forget that you are allowed to use one of the best freeware antiviruses out there. No one forces you to use it, just as no one forces you to buy Professional version.
So many people installed avast! without problems, and of course some of them are having problems. They come here in peace, calmed down, and we nicely help them to solve their problems. Do not forget that avast! technical support is also free. Where else would you get that ? E-mail, phone and forum support for free... it is our good will to help you, so show some appreciation, please. No one can even imagine how different systems could be all around the world, and which other applications people have installed... it looks like you still have traces of some other previously installed antivirus on your system. You have to be aware that 2 or more antivirus programs with resident protection enabled, installed on one system in the same time, can (and most likely - will) give you additional headaches and problems. I'm pretty sure you didn't clean your system completely... remove all possible traces of other antivirus software, clean the registry, restart the system and try installing avast! again... that's all I can say for now...
Posting your system specifications, as well as list of other security related software installed on your system, but also list of other antiviruses you had on that system, and most important - name of the latest antivirus you had running on your system prior installing avast!, could help a lot. this way, we have no clue what's going on on your side...
Cheers !