Please elaborate on the graphics set up of the system. eg, are you running nvidia graphics, what drivers are you using, proprietary or open source, version. etc.
IF you are running nvidia's proprietary drivers, after log in hit ctrl+alt+F1 (or from a rescue shell) and run the following commands:
this should reconfigure the nvidia device in the xconfig. Just for incase there is something in there that is not right.
You might also try
This should reset your cards, if a double buffer ECC (if I remember correctly) error is what is causing the screen split. This might not be relevant for your card.
If all the above is irrelevant, please post the output of:
You can get this by doing (from a console as stated above):
And copy paste the file trouble.txt's content here (it will be found in the home directory of the user logged in in the terminal)
echo "=================DMESG=================" > trouble.txt
dmesg >> trouble.txt
echo "=================X11-xORG=================" >> trouble.txt
cat /etc/X11/xorg.conf >> trouble.txt
--you can also find the path by asking 'pwd' in terminal, this will print the working directory where the file will be/was created--
If the above is not viable, you can paste to pastebin directly by doing the following steps in terminal
and then giving us the the generated URL eg:
sudo apt-get install pastebinit
cat trouble.txt | pastebinit
Cherz and good luck