Install Driver ATI Radeon V4800

Don't hold me to this but I think I may have solved your problem. Please install the Ubuntu Synaptic Package Manager. Then open it and in the search box type ATI RADEON. You should see about 40 results, most of which are listed specifically by the version they are made for. In your case trusty, and I see two of them and a bunch of generic drivers. Installing all of them should hurt nothing in so much as I understand it, only those which can work should have any effect on your system.

Please note that as much as I have loved ati cards in the past, the ati radeon cards have an awful reputation of instability and dying so if you have difficulties with it, don't blame the drivers. I can offer you some recommendations for better values in graphics cards, and one in particular which doesn't use a tiny fan to clog but instead a massive heat sink which you can drastically improve the efficiency of with a cheap $3 fan.