Running low of power steering fluid, and that often happen due to a leak from the high-pressure hose or the power steering pump, will cause the steering wheel to become hard to steer.
Broken Serpentine Belt, causes the pump to be inactive. Internal damage with the steering rack also.
Another cause for the power steering wheel to be hard to turn is a Power Steering Pump failure.
Flushing Power steering fluid in your vehicle and doing recommended schedule maintenance for the power steering system will help you to get the most of your system and avoid you the costly repair.