How to fix the power steering in an Audi A2?

The power steering in my Audi A2 has suddenly stopped working. The steering wheel has become very hard to turn and I can hear a whining noise when I try to turn it. I've checked the power steering fluid and it is at the correct level. What could be causing this issue and how can I fix it?

It is possible that the power steering belt has become worn or loose, causing the whining noise and difficulty turning. Check the belt and tighten or replace if necessary.

Another possibility is that there is a leak in the power steering system. Inspect the hoses and connections for any signs of leakage and replace as needed.