It seems very strange that you lose steering completely as the Punto steering, like all power steering, is power assisted. There is always a direct mechanical connection to the steering mechanism which will aways allow the vehicle to be steered regardless of the state of the electrics.
However, I have noticed on the Punto that at slow parking speeds (when this problem occurs mostly) the steering does "apear" to lock, in fact my wife has had trouble turning the wheel at all though I find I can steer it OK, though with great effort required! If the wheel seems to be locked but is "springy" from side to side then the car can be steered. If it is locked totally solid with no rotation movement at all then the steering lock must somehow have operated.(which i think is impossible).
Bare in mind that the power steering only operates at lower speeds and is not required at nomal cruising speed.
One of the causes of Punto power steering failure is a low battery, particularly if the alternator is not working properly. I heard of one person who only had probems at night with lights on!
Turning off the engine and restarting straight away is usually a temp fix.
My wifes problem was that as well as occasional failure (which always cleared with a restart) her battery would go flat after 4 or 5 days which I traced to the steering unit. I have worked a "fix" on that and now seeing how it goes.
Monday, 9 April 2012
Edited Monday, 9 April 2012