I installed Ubuntu 14.04 on my Lenovo IdeaPad Y510P today. Everything worked fine, but after installing my graphics card driver the background became pixelated (Nvidia GeForce GT755m). I downloaded the driver through Additional Drivers and selected Version 331.113 (Proprietary, tested). It was using Nouveau before.
When I apply Nouveau it becomes clean again, but it is much weaker when I open games, it gives me very low FPS even in Counter-Strike. With Nvidia driver FPS and everything else seems fine, except things look pixelated and when I minimize windows and maximize again, the window goes black.
I attempted to solve the problem myself by removing the old Nvidia driver and manually installing the latest version, but it did not help.
Please let me know if you need more details.