The first thing I would do is check voltage (24v) at the socket on the fixture's itself.
If voltage is present you have maybe a bad bulb or coroded connections. I cant tell you how many times just a little wiggle of the lamp fixed my yard lights. Check the transformer for how many wires, some transformers have dual (2) sets of terminals meaning one side may be bad, check voltage at the transformer. Have you been digging in the yard? Maybe the edger chopped the wire. Just a good start.