Login screen freeze

Shutdown via the Power Button and disconnect any external drives. Restart and Immediately hold the -Shift - key. This will attempting to boot into Safe Mode. It takes longer to boot and does a Repair Disk, Clears Cache File and only loads Apple Software and Fonts. In so doing, it eliminates any Third Party Software for operating. If successful - one may be able to log in. If Yes, that has identified some Third Party software that is interfering with the Normal Operation of the OS.

Should I=this not work - perform a SMC Reset as per the directions in the following link

https://support.apple.com/en-us/HT202860

So - no Time Machine Backup made ?? Not a good plan.

If the Internet Drive does not have at least 15 - 20 GB of Empty Space Available - the computer may not boot up at all. It would require Transfer files between two Mac computers using target disk mode