yesterday morning I started engine and waited for warming up. and I started to roll steering wheel after 15 min. I found that it moves only 10-15 degrees. and Wheels did not move at all.
I'm pretty sure that my p.s pump is gone. and I ordered it. do I need anything else ?? filters, sensors, etc ??

 

I would also replace the inlet suction tube from reservoir to the pump. The tube gets really hard over time and fails to make a good seal resulting in fluid cavitation.

 

If the PS pump was completely gone you'd still be able to turn the wheels (with enough strength while parked, but without so much strength while driving). Use the force.

Did you slam into a curb or something? If your wheels don't move at all with your steering wheel, you might have broken the rack and/or pinion.