So here's what happens:

I updated my system the other day, was prompted for a reboot for the update to complete but was in the middle of working so I delayed it until after I was done. I reboot and it's broken :(.

It appears to boot normally, with the following exceptions:

The purple Ubuntu load screen no longer displays (though it did for the first couple of times I tried to get in). I hear the login prompt sound, but no login prompt appears. Nor is it simply "invisible" - pressing enter, typing my password, and pressing enter again do nothing. Normally my Bluetooth mouse is functional at this point, but it is not.

GRUB displays recovery options for my current kernel, and for an older one (2.6.32-24). Trying to boot into .32-24 gives me an error saying "udevadm can't do something while udev is not configured".

So I try solutions listed here: http://superuser.com/questions/195786/ubuntu-update-went-wrong-pc-doesnt-boot-how-can-i-repair-it Nothing I tried seemed to work, and after further Googling my hunch is that it's a problem with gdm. Please correct me if I'm wrong, I don't know all that much about how Linux/Ubuntu systems work just yet.

Things I'm able to do: Boot to a live CD

Ctrl-Alt-F2 after that login sound plays brings me to a console login, which I can successfully do (it's how I tried the solutions above). This works only under the current kernel.

A hack I'd be willing to explore is removing the login prompt from the console, but I'd prefer to "simply" fix what's wrong. Like that guy, I need to repair the system rather than reinstall.

System: Dell Inspiron 1525 Core 2 Duo Proprietary Driver for Broadcom 43xx wireless

Dual-boot with Windows 7 (which is how I'm posting this, unfortunately I only have this machine and any experimenting requires constant reboots into Windows/brokenbuntu)

Last package installed was Moonlight, but it appeared to install properly.

Kernel: 2.6.32-25

Edit: After working with Karl's suggestions, it seems that the problem is with gdm.

Error exit status 245 when attempting to sudo apt-get install --reinstall gdm, also an error processing gdm when running sudo apt-get -f install.

How do I reinstall or repair gdm so that I can get back into my machine?