There are several things to do to try and break down what is wrong.

1) Disconnect the injector and connect a test light between the two pins on the pigtail and turn the key. If the light flashes than the DME is fine. And try next test.

2) Reattach the injector pigtail and stick pin in the ground side of the injector. Turn the key on and try grounding the pin to a chassis ground somewhere. If the injector clicks than you know the injector is fine. If it is fine than to the next

3)If one didnt work, but two did try this. Find what pin on the harness attached to the dme is for that injector and get your DMM out. Switch it to Ohms, and test between the ground side of the injector pigtail to the pin on the DME harness for that injector. You should read very close to zero. If you see anything over 0.5 Ohms, or OFL, than the wire leading to the Injector from the DME has a problem somewhere.

Chances are your DME has fried out that one injector and I have seen it happen, but its worth a couple of relatively eawsy tests before you buy a DME for no reason.