First I must admit that I did something really stupid.
I de-installed unity from my ubuntu 12.04 LTS to install kubuntu-desktop as I wanted to try out a different desktop environment.
The problem is that by de-installing unity it also de-installed my login screen. Apparently ldm and gdm are not included in the kubuntu-desktop package.
Now this means that when I start my ubuntu with grub, I will get a black screen after the splash screen and I can not do anything. I can't open up a terminal, and I can't press ALT + F2 to install either one of them.
The disk is encrypted and I can not access it from my windows boot. To make the situation even more dramatic: I saved the decrypt key on the same disk on a different partition.
Have I completely locked myself out? Can I alter the grub configuration so that I can get a terminal after the splash?
While typing this I just came up with the idea to boot into my other linux OS on that same disk. Maybe I can get something to work from there.