Hello and welcome to JustAnswer!
What happened when you first tried to start it and it wouldn't start? Did it start up and die a few times? Or crank but not start at all?
Turn the key on without trying to start the engine and take note of what the fuel gauge and voltmeter do. See if they work or if they are staying down now that it won't start.
All are staying down.
For whatever reason your powertrain control module (PCM) is down. This is the module that controls the engine. This can be an internal PCM problem or external. If the PCM loses a power or ground feed, if the sensor ground circuit shorts to voltage, or if any of the 5v reference circuits short to ground it will take the PCM down.
It's going to take some electrical testing to see what is going on for sure. If you have a 4.0 engine a very common cause of this is an internally shorted crankshaft position sensor which takes the PCM down. If you have a voltmeter and are able to do some electrical testing I can help you determine what is going on.