My 1999 GMC sonoma won't start. I changed computer, distributor cap, rotor module, coil, key switch and crank sensor- no luck. My next thought was ignition box, unless there is a better suggestion?

My first concern is: how do you know there isn't fire? Did you
1- Check it with a screwdriver inside the spark plug wire at spark plug end to ground. This isn't the right way.
2- Have you check fire with HEI spark tester.
(The right way). To see a spark with the tester there will be 25k the spark to jump to ground and it test the coil working properly.
Now the fire system or ignition spark work this way.

When the engine is turning up to 400rpm the camshaft gear inside the engine makes distributor shaft turning. We often see the distributor gear at the end worn like an eaten apple.
Remove the Dist. Cap Somebody starts the engine look for the rotor if it turns. This will tell you the gear is OK.
P.S; What you call the SENSOR = Ignition Module just to let you know
Hope it helps

have you replaced the ignition control module in the distributor

Check for power to the ignition module. That is the most likely part to fail after the coil.

Several things can cause this problem, cracked distributor cap, old ignition rotor. Or if you have coil packs, cracked coil pack, ignition control module, crank position sensor, cam position sensor. Coil pack parts and sensors can be checked by autozone, cap and rotor will have corrosion on the rotor, however a small crack in the distributor cap can be next to impossible to see, replacement is usually best option.

you said you repl dist cap that means you don't have a crank sensor you have electronic ing module. remove your elec ing module have it tested most auto parts stores could test your module, or check your coil at the neg terminal. should have power. if not you lost your primary volt from your batt.your secondary power is coming from your electronic ing module from the module to the pos terminal on the coil, when the eng cranks,from the coil to the dist cap , from the dist cap center to the rotor then out to the plugs,this all happen pervided the timing belt or timing chain is ok. the cumbustion chainber needs 3 things , thats fuel, air, and spark.

If there is no spark at the spark plugs, check for spark coming out of the coil. If there is spark coming out of the coil, replace your distributor cap, rotor and spark plugs, and spark plug wires. (Do a tune up)
If there is no spark at the coil, the most likely cause would be the crank sensor or the ignition control module.

Check for injector pulse if no pulse with no spark check ignition module in distributor or crank sensor.

Sounds like you may have a crank sensor or a ignition module,or pickup coil gone bad,you should use a scan tool to look for cranking RPM's,or pull your distributor cap and look for a green corrosion on the pickup coil wires at the module.

sounds like it could be plugged injectors or a timing problem.

Check you Cranckshaft Position Sensor....i have a 99 GMC Sonoma and i had the same problem. It would not start in the morning, and i replaced everything i could think of. ignition coil, distributor cap and rotor, wires and plugs and no luck. I could hear the fuel pump prime when i turned the key on, so i knew it was getting fuel. As it turned out the sensor (which is located on the front and bottom of the engine block just behind the Crankshaft drive belt pulley.) and was preventing the engine from starting. Check that out and that may be the cause of your problem