i have installed ubuntu 12.04. while i'm using the screen goes off, comes back on (during which time, the system is not responsive) and this process repeats one more time in immediate succession after which the computer is responsive again. sometimes the system hangs indefinitely. sometimes the windows go blank. only the title bars are seen. i have tried re-installing the OS three times with no improvements. i have tried both 32 bit as well as 64 bit. i have no idea what the problem is and have tried hard to pin point that. i never had this prob till 11.10 my system config is as follow processor - 2nd gen intel core i7 (2660k) graphics - intel onboard HD graphics 3000 (no external graphics card) RAM - 4GB none of my friends seem to experience this problem. it really gets annoying as it happens really often. please advice