There's a critical ground wire attached to the thermostat housing. If it's loose, corroded, or disconnected, the engine won't have spark or fuel and therefore can't start. Check that ground.
If the ground is fine, then turn the key to ON(II) and listen carefully for the low humming sound of the fuel pump priming for 2 seconds in the rear. Do you hear it?
Next check for spark using this
method.
Any CEL codes?
Also make sure you connected the plug wires in the proper firing order on the distributor cap. The cylinders are ordered 4-3-2-1 as you go from the distributor to the timing belt.