I know what you mean about computer over dose. I have a laptop so i will put it on the floor or a stool in front of me or I will pull a lounger up to my desk top. If you gt out of your usual computer siting position and change the environment.... put on soft music.... light some candles.... burn incense. Those kinds of things that you might do to meditate normally.

There are lots of books about mandalas. Maybe even in your local library.

Let us know how it goes. Remember to make sure your breathing stays even and be patient. Just keep looking at the centre.