How can I reboot my managed Linux PC?
NEVER reboot your workstation. Maybe there are other students logged in and working on it or any important jobs running. Probably it is only your crashed browser that blocks the keyboard or mouse. Login from an other machine and find out which process is locking the machine up. Try top to figure this out.
On a Linux Workstation you can use the key-combination Ctrl+Alt+Backspace to restart your Xserver.
A very effective and simple way to 'unblock' a machine is to walk to one which is working and then type:
ssh username@blocked_machine kill -TERM -1
If you still have problems, mail to firstname.lastname@example.org