check the power steering fluid first, with the engine switched OFF, vital and first point of call.
If it is low, then your power steering pump is running dry, and "mashing" up the gears, so go outside and check that item first and immediately.
If the fluid level is good, and if the colour looks normal, then it could be that either
1) the belt is slipping and not driving the pump
or
2) the pump has become "lunch" internally