oil pressure

If I can't get oil pressure up after priming the pump, what else could be the cause? The oil pump is new, could it be bad (i.e. pressure relief valve?
Could the machinest not have cleaned the oil gallies and they are plugged?
Is it possible that the main bearing is installed incorrrectly and the oil hole is not where it should be?
Any thoughts on this or other isues would be greatly appreciated since I don't want to yank a pan/engine unless I have too.
This could drive me to drinkin, maybe I shouda got a hot-rod Lincoln.