2008 XC70 power-steering problem

Hi All,

Last week my XC70 began having problems with the power steering when I start the car. Almost half of the time, the power steering pump (I'm guessing) doesn't start when I start the car. If I turn off the car and re-start it, things are fine. Has anyone else experienced this problem? Do you know the cuase (is it the computer or mechanical)?

Thanks