Step away from the computer. You should only approach it when you have an idea. Cleaning house. Sounds weird but it's a physical activity while the mind is on auto-pilot. If you still have artists block, hey, at least you've got a clean house. One of my favorite exercises is the "eight minute stream of consciousness". Pull out a piece of paper (or open notepad) and write / type non-stop for eight minutes without reading it. Try and stay away from "I don't know what to think about"; more along the lines of "I had a funny dream last night...." or something like that. I can only go for about 5 or 6 minutes before I peter out (excuse the double and triple entendre), but you'll be surprised when you read it back.