Hello blue_fyre and welcome to the forum.
Often times when someone is having difficulty with an AV it is due to other things. So let's trouble shoot to see what is going on. First I need to know the following:
1. What is your OS, 32 or 64-bit?
2. What version of Avast did you install? 5.0.677?
3. What product of Avast did you install? Free, Pro, AIS?
4. What other security software do you
currently have or did you have
in the past on this machine including antivirus (AV) and other security programs (including trial software or AV's)? If they were in the past, how did you remove them (the vendor's uninstaller's tool or another way)?
5. What browser(s) do you use? Is the problem happening in one or more browsers?
6. When you uninstalled Avast, did you use the Avast Uninstaller Utility Tool in Safe Mode?
7. Did you have a previous version of Avast on this machine? If so, did you use the Uninstaller Tool in Safe Mode to also remove this prior version as well PRIOR to installing your current version?
8. Other than this problem, is your machine acting normally?
Thank you.