Dell Inspiron 3521

Hi. I have got a Dell Inspiron 3521 which is Ubuntu Certified. Spec.: CPU I3-3217u, GPU HD 4000 integrated, AMD 7670m 1gb. I do not like Windows 10, even I hate them. I wanted to use Ubuntu 14.04 so I tried to install them. It was succesfull, but when I restarted the system, it was very slow. I wanted to install the proprietary driver of the AMD GPU and it said the installation was succesfull, then I restarted them, but after that the system became unstable. The crashes were usually and a lot of program did not want to work because of libGL error...I can not remember them because, after I tried every possible solution in wain, I have installed Windows 10, but it is a disaster.