Not a GRUB problem, since it starts to boot. I've had this problem in the past due to video driver changes, usually when trying to install or, more likely, uninstall a proprietary driver and having some problem. The fix was very easy once I discovered the problem. I replaced the file /etc/X11/xorg.conf
with the default. Last time it happened, there were several backups, named xorg.conf.xxxxx with xxxxx being backup names like original-1, fglrx-0, etc.
If you have backups dated before your upgrade, you could try renaming the current file, then copying one of the backups to the original name. You'll need to use sudo, of course, to do this.
The default with no proprietary driver is under 10 lines. I have one for AMD/ATI video, which you could use if you have that. If you have nVidia, I might be able to find one of them in my other computer.
I think you can generate this file by entering the command dpkg-reconfigure xserver-xorg
, but I haven't used that in a long time, so I'm not sure if it still works. Actually, I'm not 100% sure if it ever worked. :)
You can do this from a virtual terminal. Can't hurt anything if you're careful, and it beats reinstalling - something I rarely have done.