If the starter turns over then it may be that you need to replace that but if it doesnt even turn over then the battery may need to be replaced.

I have had this problem because I just purchased a 93 Grand Cherokee limited with 145K on it. It ran fine for 2 hours, then ran crappy for an hour, then died and would not restart. It had sat for a long time before I bought it. It had multiple problems. A list follows of exact symptoms and tips. 1. It would start when cold, run three seconds, then die: cause: Alarm system was shutting off main relay. Slolution: under the driver side kick panel, find the yellow and purple wire, SPLICE into it, and ground it out: this will disable the alarm system. 2. Would run for a few minutes, then mis out and eventually die. Problem: clogged fule filter: easy to get to on the early models. 3. Would not start until the igniton was on long enough to let the "check engine light" to come on, then it would start: this was sopmtimes acompanied by a buzzing or machine-gun type noise from under the hood. Problem: Pin number in the computer wiring harness socket was corroded in two. Could not repair: had to replace whole computer $$$. 4. Intermittentily bucks and coughs going down the road: problem: Detrius inside of distributor cap: always buy cap and rotor with brass parts: aluminum does not make a good electrode, and will cause problems inside the distributor when it starts to wear or corrode. 5. Then the vehicle would start, and run really good cold: but as soon as it would warm up, it would not run, and eventually die, and not restart unless the throttle was held to floor, like it was flooded; Problem: the coolant temperature sensor was bad: this is the new equivelant of driving a car with a stuck mechanical choke. This sensor IS NOT the same one that drives the guage on the dash: the computer does not use the gauge sensor, and vice-versa.

first check ASD Relay to see if power supplies to coil and injectors while cranking. if that is ok then I'd look at the crank sensor.