Well, that'd depend on the type of pump you've got. I'd assume the gears are in backwards or something, or there's now an obstruction where the reservoir drains into the pump, or something like that. Could be something as simple as a mismatched gasket set, too.
Also if I remember right, it takes a LOT of bleeding to get all the air out after you change the pump. Lots of shuffling the steering wheel side to side...try unhooking the return line and stuffing it in a 2L bottle to see if you're actually getting flow thru the system I suppose. Make it a clean 2L and you can pour it right back in when you're done. If ya got flow, I suppose you can unhook the feed line off the rack, and turn the pump by hand or with a slow speed drill to see if you've got flow there. If you keep moving up the line and find that you've got no flow coming out of the pump, chances are you've done something wrong with the rebuild.
If you've got flow, I'd guess the next thing you'll be rebuilding is the rack

though honestly I'd recommend just getting a new one, either out of a junkyard or from a parts shop. That goes for almost any rebuildable part, though. Saves a lot of hassle.