If you aren't getting spark to the plugs, the first thing I would check is the CPS (crankshaft position sensor), located behind the crank pulley. It'* a pretty common fail point for many GM models, as it is subjected to heat and debris. It'* also a common cause of stalling when hot, or hard-to-start when hot, but as the sensor gets weaker it can lead to an intermittent no-start problem.
The crankshaft position sensor tells the computer the engine is physically turning, and tells the ignition module to produce spark. If the ignition module doesn't get this signal, it will not send spark to the plugs. You will most likely have to remove the serpentine belt and vibration dampener (rubber-filled pulley on the crankshaft) to access the sensor.
If you're replacing the crank sensor, you might as well splurge for the vibration dampener (harmonic balancer) as well - the dampener on my '87 LeSabre went, and I splurged for the CPS as well since I could get to it easily with the old dampener off. And, like I said, it'* a common fail point.
Hope this helps you out; if not, we can troubleshoot further... Ignition module or coil could be bad, but that would be The Next Step.