I'm having the same issue with a computer that uses a Microsoft account, i.e., not a local account, but one based on a gmail address. The account is good, as I can use it to get here.
My desktop PC has been running the Windows 10 Insider edition for months with zero problems, and this afternoon, it finally got around to let me install the GA version. Once it finished and rebooted and all, it would give me the login screen. If I attempt to login with the same ID/password I used before, it never completely logs in. The main screen flashes around , I can 100% CPU, mostly Windows Defender, but the machine never gets to a point where I can use the keyboard, other than CTRL-ALT-DEL. No icons are displayed, and the cursor is always "working".
I'm going to back to my previous build. Shift + Restart