Some extra details would help.
What car do you have? Is it the stock rack? Did you bleed the system when you changed the pump? Is there enough fluid in the system?
1) I've got a 2004 WRX wagon
2) It's a stock power steering rack
3) No I didn't bleed the system after I replaced the power steering pump
4) Yes i filled the reservoir with fluid after I changed the power steering pump
thanks