If you're using the computer for revising, I tend to just open the windows I need to begin. Then I close or hide the Windows taskbar to stop any temptation to open other programs - which are the main distraction.
Or even better, just don't use the computer at all. I have textbooks for all the subjects, and it can be useful to go into a peaceful room and just do something active (take notes, create questions, do a spider diagram, etc.). You can always find something better/more interesting to do than revision; it's just a matter of disciplining yourself and sticking to it. Try creating a schedule so you know exactly when to revise and when you can play games or watch TV.