I started my car this morning and backed up out of my parking spot. When I left the parking lot I lost steering (the response from the wheel is extremely stiff and behaves as if there is no power steering.) There are no leaks indicating loss of power steering fluid and the reservoir is full, so I am at a loss for ideas. What do you think could cause this?
Depending on the age of the car you may be experiencing "steering rack morning sickness". If it gets better as the car warms up you most likely have a steering rack that is on its' way out. This is a common first symptom of rack failure. Generally it occurs after the car has sat for an extended period like overnight. It will get gradually take longer and longer for the power steering to come back. At some point the power assist will fail. Since steering is a pretty important function you should have it checked by your mechanic to verify that nothing is near immenant failure.
If everything in the power steering system checks out, it could be a binding U joint: http://my.cardone.com/techdocs/PT%2027-0007.pdf