You can about several ways to try and fix this.
First off open a terminal and run
Copy the contents.
sudo gedit /etc/apt/sources.list
In the forums "new" reply section, click on the #, which is for code.
Paste your copied content inbetween to two [code][code](/symbol omitted)
This will help us in the forums understand what's going on in line 68.
Another thing that I do whenever I mess up my source.list is change it in the update-manager.
Open the update-manager and in the left-bottom corner click on settings.
Move into the "other software" tab and uncheck absolutely everything.(The first one will prompt you for your password, but that's it.)
After unchecking all the checked repos in other software, close(not revert) and then click check in the update-manager.(this runs an update.
From there we can begin to fix any bad video problems, or at least try.