Have you cleaned the back side of the brew head screen? You need to remove the phillips-head screw in the middle (be careful not to strip the head); if you're using very finely ground coffee often it can get behind the screen and clog it. If this doesn't fix it...
Will a stream of water come from the steam wand when the machine is cold? If so then your pump is working. If it's only coming out when the machine is hot then it's just the pressure from the boiler pushing it out and you may need to replace your pump. This machine uses an ULKA EX5 and it can be bought from espressoparts.com as well as other online retailers. Pumps dying on these machines is fairly uncommon however so I would make very sure that's the problem before ordering a new one.