I assume you are running Debian???
Can you try CTRL+ALT+F1
This should give you a full screen command entry.
Enter your user name and press the enter key.
Then enter your password - no characters will appear to be entered and press enter.
You should then be logged on and you can enter commands such as
This shows disk usage on a per file system basis.
If you see any high percentage disk usage then it would be worth pasting the details on this forum.