1995 Toyota Corolla power steering

Steering problem
1995 Toyota Corolla Two Wheel Drive Manual 53068 miles

my car is a 1995 toyota corolla. I just purchased it last december 2007. The first thing I noticed I everytime im parking the car on reverse and manouvering the steering either left or right, it becomes so hard that you can consider that it is no power steering car. Sometimes on occassions, the steering reverse manouvering is running good. I just don't know if the alternator is not charging appropriately or it involves the power steering. Power steering reservoir is regularly refilled. Kindly help on what should I do in order for me to determine the problem. Thank you.