I'm with Ashman on this. Whenever you do some work and something that was working fine, ceases to work fine, go back to the area where you were working. Check your battery cables. Did you knock something loose somewhere. I would expect that a thorough, visual inspection would turn up the problem. The odds are not very good that the starter just decided to quit at this particular time.
If the visual inspection doesn't turn up anything. Check for voltage at the big cable on the starter. It should be there even with the ignition off. With that voltage there, hook your voltmeter or test light to the primary wire to the starter and see if you have voltage when you turn the key. If not trace the circuit backwards, especially the neutral safety switch like MB Doc said.