Answer
It could be many things but it depends on what you mean by "won't run." I would need a little more background information. I will assume that it was running, and you parkd it, and then would not restart. Did it crank, or click, or do absolutely nothing? If it cranks but does not start there is a 90% chance that it is an ignition problem. Since the LS400 engine uses 4 cams and two distributors, that is an unlikely scenario. If it clicks you need to have someone look at the headlights while you turn the key. If the lights dim noticeably when you try to start it, it is either a problem with the battery terminals or the battery itself. In a worst case scenario the starter could be gone but it most likely would have given some indication of problems. Starter problems are very limited with this car, not unheard of, but very uncommon. Most actual starter problems are due to worn contacts on the starter, but not the starter itself. Thie would not be a big issue except that the starter is located UNDER the intake manifold, it is a very big issue to service. If NOTHING happens (no crank, no click, no headlight dimming) it might be the neutral safety switch. You can check this by trying to start it in the NEUTRAL position.
If you tell me more details I will try to help. My guess is that if your battery is 4 or more years old, it may be the problem.
Denny
First answer by Vbdenny. Last edit by Vbdenny. Contributor trust: 279 [recommend contributor]. Question popularity: 47 [recommend question]
