Cat 953 won't start

I lucked out and bought a pretty decent 953 track loader from a construction company getting out of the business. It spent most of it's life digging basements. It's got 4000 hours on a new motor and 12,000 hours on everything else. I bought it to clean up an 80 acre farm and to drive fence posts. It's my first track machine and the first one I've ever run. I apparently made a rookie mistake of getting stuck in a drainage ravine. Somewhere in the retrieval process, I lost the access panel so a bunch of mud ended up around the engine as well as the fan throwing water everywhere. It drove fine from the ditch to the house, but now it will not start. All the lights work, the fuses are good, but the starter will not kick in. I'm looking for any ideas of where to start troubleshooting. Any thoughts will be greatly appreciated. Thanks.

Access panel.

Hello.

OK, what we have a set of switches all grouped together that is called the ignition switch.
There are actually 2 circuits feeding it.
The first is accessory, and, as the name implies, switches on accessories.
The second circuit is the actual ignition circuit, off, run, start.
If power is not provided there you will not have voltage on run or start.
Now that we have checked that, switch to start and you should have voltage to the starter line.
Next is the starter relay, or starter solenoid as they are normally called.
http://en.wikipedia.org/wiki/Starter_solenoid
You can jumper the starter with a screwdriver, but be VERY CAREFUL people have been killed doing this very thing, the starter will crank in gear!!!!
Anyhow, carefully break it down into small parts to find the problem.
Let us know on your progress and if you have any questions.

Check for the obvious first. Battery voltage? Loose or damaged connections? Then you can start isolating the issue....... I personally suspect that starter.....

Thanks for the replies. I originally thought the batteries were low, but I charged them completely. I'm really leaning toward a ground somewhere. Hopefully it's not a starter, they look expensive.

also check safety switch

I have dealt with this once before. A genius got his dozer stuck in a mud hole and water got up to the starter relay and the starter. Electrolysis corroded the relay contacts and rust froze up the solenoid and carbon brushes in the starter. We replaced the relay and I fixed the starter. The screwdriver or jumper cable methods work well to test the starter. If the starter is not working take it apart before buying a new one or getting rebuilt.

just going to poke my two cents in here guys.... how is the ground? corroded?

Just wanted to drop a note and say thanks for the advice. I finally got it fixed. I tried using a wire to jump across the starter, but that didn't work. It did generate lots of sparks. I ended up taking the starter off. The bolts holding the starter were loose (my opinion) and apparently the gasket had failed letting water seep/drip on the shaft of the starter. It was rusted so that the gear wouldn't engage. I wanted to have the starter tested before I bought a new one, but I had the hardest time finding a place that could test a 24 volt starter. I finally found a guy the local Cat dealer (apparently they don't test either) knew. He sanded the shaft a little then sprayed some penetrating lube behind the gear, then switched it on. It engaged, but you could tell it was still sticky. He continued working until it engaged smoothly. After I got it back together, it started right up.