Dead crank or cam sensor or if you have a distributor, I'm guessing pick-up coil.
Crank/cam sensor control spark timing and fuel injector timing. In the case of spark timing, its just like the pickup coil.
Pick-up coil in a distributor relies on a reluctor wheel to make an electrical pulse signal across the pickup coil reader. Without the signal, no coil firing into the distro. Since you have spark only on plug 1, its possible that could be what's going south on you.
Got a Check Engine Light on? You could stomp test it and get a code for the crank/cam sensors if they're at fault.