Power Steering - or lack of!

[Pierre2]

Hi,

Apologies if this has been covered but I'm new on the site!

Three or four times over the past year this has happened:- on starting the vehicle the warning bleep sounds "Check Handbook" flashes up and the steering is as solid as a rock. Fearing the worse I turn the engine off, restart and all is fine. But is it??  The only suspicion I've seen written is 'low battery' but the Battery is relatively new and when the old Battery was failing after 7yrs use, it didn't happen.

Is there any risk of it failing whilst driving? 

My nearest Sub garage is 100 miles away but two garages locally have found nothing anyway!!

Any advice please??