I called Apple Support for help in adding space to download my new tax software. She helped me by removing items and also had me change my ID and password. After 2 1/2 hrs, a pop up came on the screen asking for my key change password. I have no idea when I must have put it in but cannot find it. When asked to put in the password in the past, I simply closed it and ignored it. Now, I cannot cancel it and cannot access anything. My MAC Air ( OS 10.13) is essentially locked down. She said that I had to go an Apple Store (1 1/2 hrs away) or a Best Buy to fix it. I also need to buy an external HD to move the contents of my Mac to allow the addition of a new OS ( Big Sur). Any thoughts.