I am not sure if this will help you or not, but what do you have to lose by trying it! A couple things you can try first. 1.) When the login screen shows up in the "Administrator password section" type in (admin) as the password. 2.) Just hit "Enter". And if all of these do not work, make SURE that you pc is completely turned off. Now reboot it and when the & when the Windows Logo screen that has the bar that goes across the screen, IMMEDIATELY SHUT it down either by hold the power button down or just unplugging it! Now reboot it again, you should get the screen that tells you that "Windows, had an error and could not boot" or something like that & you are given a couple options like: Safe Mode, Safe Mode with Networking, Last known Good configuration. I suggest that you use "Safe Mode with Networking" once you click that it will load/check Windows files to make sure that they are ok. Then you are brought to the "User Menu" at this point Administrator should be listed and not have a password required. It this is the case then go in and make the necessary changes to Avast & also to the Administrator User account. If the Administrator does have to have a password, your user account should also show up on this screen & if you have/had a password on your account type it in and once (HOPEFULLY) you are able to get into your account, you can un-install avast or even better use System Restore to take it back a time prior to this problem. Luck!!!