Thanks alot EDDY1! I fixed it.
The Shift key didn't do anything for me, but I deleted the "#" in /etc/default/grub on a line that said something about graphic mode in 640x480. Thanks alot for the hint
EDIT: To be exact, this:
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'