Unable to login laptop running Vista 64-bit AFTER installing Avast free

I’m getting error message letting me know there has been an unauthorized changed made in windows.
Prior to install, I unistalled AVG, rebooted then downloaded AVAST free from cnet/download. I selected to install Google Chrome as my default browser, and planned to unistall Firefox. Now, I’m unable to access my laptop. I’m given a choose to locate error online, at a microsoft address, but unfortunately, that URL is unresponsive.

Thank you for any helps.

Just had this issue on my other PC. Luckily I have a 2nd one to research the issue. Please find information regarding the issue here http://social.microsoft.com/Forums/en-US/genuinevista/thread/5e6d2437-2427-4c8b-a7cb-622bbe028ca4

Quick fix would be to restart the laptop in Safe Mode, uninstall Avast!. Restart your laptop and go to https://support.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=730, which is the Avast site and download the uninstall utility for Avast!. Restart the laptop in Safe Mode and run the Avast! uninstall utility to make sure everything is off your hard drive. Once that is complete restart the laptop and install new a/v software immediately. Since you were able to post here after the issue came up I will assume you have another computer you are using to access this forum. Search CNET for free a/v programs.

According to Avast!, Vista must be updated to SP2 in order for this issue to not appear. I’m currently in the process of updating my OS but don’t know if the issue will occur again. I have used Avast! free for years and have always recommended it to all my family and friends. I am really disappointed with this latest version and the fact that this issue does not seem to have been addressed in a prompt manner. I am considering removing it from mine and my other family member’s computers/laptops and using another a/v program.