Several things cause AV's not to install properly. You either have remnants of a previous security software on your machine, you have malware on your system, or something is corrupt with your system...to name the most common.
1. You claim you removed the AVG from your system...right? Did you reboot after doing this? If not, run the AVG uninstaller tool again and REBOOT.
2. Did you have any other security software on your system, even if it was a trial AV? What is your FW? What other security software is on your machine?
3. Are you MS Updates current?
4. Is your machine acting "normal" otherwise?
After you confirm that you have no remnants of security software on your machine and that your MS Updates are or were current, then please try the following below:
Uninstall and a
CLEAN install of Avast:
1. Save a copy of newest version of Avast (5.0.594) for the version you need and save it to your HDD:
Free –
http://files.avast.com/iavs5x/setup_av_free.exe 2. Download the Avast Uninstall Utility, aswClear5.exe
http://www.avast.com/uninstall-utility and save it to your HDD (it has uninstall tools for both 4.0 and 5.0).
You will need to uninstall BOTH v. 4.0 and 5.0.3. Disconnect from the Internet at this time.
4. Uninstall Avast through "Add/Remove Programs" through Control Panel (if possible).
5. Boot into
Safe Mode (hit F8 repeatedly) and run the Avast Uninstall Tool.
6.
Reboot.
7. Install the newest version of Avast and
reboot twice.
8. Get Internet access and update Avast definitions.
9. Register your copy or add the license key for Free
http://www.avast.com/registration-free-antivirus.php.
Should this fail, turn on Windows Defender as
resident and
update your definitions so that you have AV protection.
Please report back to us. Thank you.
Edit: This is the new download for Avast FREE version 5.0.677:
Free –
http://www.avast.com/free-antivirus-download#tab4