Stiff power steering problems?

My car has been giving me some steering problems lately. When i start the car in the morning, the steering feels normal and light. But after driving for a small period of time, it becomes really heavy and difficult to use 1 handed. Any reason as to what could cause this?
PS. The car is a 2004 Ford Falcon(Australia)
Cheers, Reece

Have you checked your power steering fluid level? If yes, and it's ok, you may need a new power steering pump.

Reece, what "voterepublican2002" said is the first thing you should do and should be the most obvious since that is the most common. Cause of this is usually a leaking power steering hose which isn't too hard to accept at the repair shop in terms of costs. If your power steering hose isn't leaking, then then next thing you do is check for leaks around the steering rack. With Fords, this will happen occasionally. If you see fluid leaking there, then its a matter of replacing the steering rack. This is definitely not a job for an amateur or a "backyard mechanic" unless they've had specific training in this area. Getting this replaced in a timely matter is required. If it isn't then it can ruin your power steering pump and then both will have to be replaced. The rack replacement is hard enough to swallow in terms of costs but to have the power steering pump added on to the ree
repair bill is adding insult to injury. So to summarize, check the power steering fluid level; then check for leaks at the power steering hose and steering rack; if any of those are showing leaks, then its time to get them replaced. In terms of repair costs, power steering hose is least expensive; power steering pump is middle expensive; steering rack is most expensive. Hope this helps and best of luck.