Same problem here.
1)It says I'm already registered, but since I uninstalled 4 & installed 5, I shouldn't be.
2)Nothing happens when I push "Fix Now" or "Start Program."
3)I've already gone to Start/Run/MSConfig to make sure Avast was checked.
4)I've tried to force-start it with Start/Run/Services.msc, but it refused.
5)The repair option didn't help. Neither did reinstalling or trying to update the program.
6)It seems annoying to have to download the special uninstaller, reboot in safe mode, uninstall, reboot in normal mode, then reinstall. You'd have to defrag after all that too.
7)There seems to be an endless amount of people complaining about the same thing, so clearly there is a bug & it needs to be patched.