Power Steering problem

Hi guys I have a 1996 Toyota Camry, 156,000 mi, 4 cyl. About 8 weeks ago my steering was acting a little different (stiff at times) and when I would turn really really sharp it would screech. Then just a few days ago my power steering is going in and out of working and difficult to steer. The fluid level is fine and so is the belt. My husband jacked the car up and looked at the pump and the rack. We really arent sure which one is the problem and can't afford to replace both. Is there a way or signs to tell us if it is the rack and pinion, or if it's the PS pump? How can we tell which one is the problem? Thank you so much! Janette :wink: