What do you do after entering your user name and password?
You should get a user prompt at that point ($). Did you type;
?
That should take you to a desktop if all is well except for your DM which runs the gui login.
When you reach that log in and get to a tty prompt you can change to root using;
or by simply booting to recovery and giving your password should get you to root prompt (#).
Did you try;
and
These are not likely to get you any needed upgrades but may give errors that shed light on the problem.
You could also, to see if it is simply a scrambled package problem, try;
It is possible that there is some problem with permissions for your user. You could, although this is not encouraged, run, at the root prompt;
If that takes you to a desktop it would indicate that there is a problem with your user. You should be aware that you are, at that point, logged in as root to your system and anything you do will be taken as direction from the root user and you can totally screw your system. I will show that your system works. You could at that point log out and attempt to deal with this with more information.
That is about all anyone can tell you with no more info than you provide. When you boot to recovery, I know the screens scroll by fast, but did you see any errors?
If you did not try "startx" at the tty log in that is the place to start.
Take notes. Think back to the last time the system was up. Did you do anything different? Were there errors on the screen when you shut down?
Have you looked at any of the log files? This can be done with nano a command line text editor included in all Debian installs?
I believe your system should be using MDM as the DM. Have you tried;
at a root (#) prompt?
Something has obviously gone wrong with your system. There should be some indication of it somewhere. You need to look for it.
The information you give can be summed up as; it ran for 2 weeks and now it doesn't. This is not something to base an idea on.
Did you shut down ever in those 2 weeks? What were you doing when on it. Have you added packages to the system and were there any irregularities to any of those installs?