I followed somebody's advice,and turned off openGL. Now everything is fine. thank you Twistit Saiman.
I have just bought a new laptop Studio 1555 : Pentium Dual Core T4300(2.1GHz,800MHz,1MB) Graphics : 512 MB ATI Mobility RADEON HD 4570 All kinds of lines and prisms keep appearing on the screen all the time. Would anybody know how to get rid of them?