Avast 6 installation issues

After installing avast 6.0 eventhough the installation was successful and avast icon was in the tray icon when windows is restarted there is a problem. Windows reboots again & again when it comes to login screen. (Windows XP with service pack 2). It was working fine with avast 5.0 before.

Did you have any antivirus before avast? Or, do you have any antivirus running alongside avast?

Please read:
Support for Windows XP Service Pack 2 ends on July 13, 2010
http://support.microsoft.com/gp/lifean31

XP SP3 provides many system Critical Updates and many performance enhancements.

I have installed only Avast 6.0 and there is Firewall (Zonelabs) which is already installed alongwith Avast 5.0 and running without issues.

On XP, you should use 6.0.1027 pre-release to prevent compatibility issues with ZA.