I can not login in "graphical mode" on a linux workstation, but I can login in "text mode" ...
I can not save files or create a new one... on ssh.sissa.it too
Probably you exceed your quota (your disk space usage) on the file system of your sector.
Check your quota usage using the command: quota
If you exceed your quota, you have to delete some files. PLEASE DO IT CAREFULLY.
For more information please read the page about disk space usage.
If your graphical configuration is damaged, ask help to helpdesk staff.