Computer freezing at login page, won't complete boot

[betwixt]

Hi everybody,

I restarted my Thinkpad T61 yesterday after upgrading firefox in the terminal, and the login screen was frozen so I wasn't able to enter my password. I tried several more times, including running the recovery mode boot, to no avail.

Any idea what could have happened or what I can do about it?

Many thanks!
Arbor