Mini Cooper - power steering pblm

I have an '03 Cooper and the power steering comes and goes. It can be there when I start the car and then go out at anytime while driving or it may not be there when I start but after I shut it off to go in to a store it will there when I start it again. The frequency varies - this may occur every day for a week and then it will be fine for 10 days or so and then show up again. Any ideas?

common problem with the minis. Do a search on here or on a mini web site or google and see the many hundreds/thousands of posts on mini PS problems.