Can't login to windows after AVG request to update and restart

I had just logged in and started up my PC. (I have 4 for different reasons) After about a minute I got a typical AVG update window pop up request to update/ restart AVG. Since I had not started any other programs I selected the restart option.
Computer shut down, restarted and then the user profile login window popped up. I put in the same password I used less than 2 minutes before and I got an error message that the password is incorrect.
I have checked for caps loc error re-checked the password, slowly typed the password one key at a time, changed keyboards, etc. Nothing lets me login. Now, I just got the same message on this computer that there is an update available for AVG on this machine. I am afraid to update because I might lose access to this machine. What should I do?

Hello Mark,
I understand this must be disappointing you, let us know which AVG product you are using and if possible provide us screenshot of that pop-up you are getting in order to assist you better. Please feel free to contact us for further assistance.
Thank you.

Hello Mark,
I understand this must be disappointing you, let us know which AVG product you are using and if possible provide us screenshot of that pop-up you are getting in order to assist you better. Please feel free to contact us for further assistance.
Thank you.