I have been using avast! 5 since it was first released without any problems whatsoever. I believe that the vast majority of people who install and use it are doing so problem free. That is, however, not to say that there is no possibility of something not working correctly for you. No software is absolutely 100% perfect.
In order to maximize your chances of a problem free install I would do the following:
1. download the latest avast! 5 Free package.
2. download the avast! uninstall utility (awsclear.exe) from this website -
http://www.avast.com/uninstall-utility3. uninstall your current avast! 4.8 using the Control Panel -> Add/Remove Programs
4. reboot into Safe Mode
5. run the awsclear.exe uninstall utility
6. reboot normally
7. install avast! 5.0 Free
8. reboot
Note that Vlk (one of the avast! developers who posts on this forum) has said that it is not necessary to do the above steps to get a good install of avast! unless there is a problem with the initial install. He obviously knows more than I do, but I would still follow the above in any case. I'm just the cautious type . .
You should now have a perfectly running copy of avast! 5 Free. If you have any questions or problems, come on back and post again in the forum.
Good luck . . .