It is likely you have run out of space on the local drive of the SIMS server. You can go to a file or domain server and in windows explorer type\\servername\c$ of the SIMS server. This should take you to the C drive, if it is not your C drive, could be D or E or another drive.
The path should look similar to this
E:\Program Files\Microsoft SQL Server\MSSQL13.SIMS2016\MSSQL\Backup
Most likely culprit are the .bak files that are created when you run a SIMS update, if the updates have been successful, then you don't need to keep these files. You have stated you have done an update and this may have used up the space on the drive.
I have had this problem a few times and once I have cleared the BAK files, its fine (To be safe, copy off the BAK files to an external drive only if you can get that far)
Delete the oldest BAK files first not the newer ones just to make sure you can then log on and the system does not freeze
Hope this helps
