1985 Nissan Sentra • 210,000 miles

I've got an '85 Sentra 5 speed, 4 cylinder, gasoline engine, with 210,000 miles. I was driving tonight, going about 30mph, when all of a sudden I started hearing a grinding noise coming from under the hood, it started getting louder, and then the engine died. I pulled over and opened the hood, and nothing seemed unusual or out of place. Radiator fluid was low, and I have had a slow and small leak in the radiator lately, but the oil was full and just changed last week. I tried starting it again after about 5 minutes, and the starter was turning over, with plenty of voltage, but it wasn't turning over the engine, and there were weird clicking and light grinding noises. I left it sit. My immediate thought was that maybe the timing belt or chain snapped.I'm not well versed on this, especially changing one of those if that's the case. Also, I don't see why, if for example, it overheated with no warning light, the engine wouldn't at least turn over. Any help would be greatly appreciated!
February 19, 2013.

Remove the distributor cap and have helper crank engine over: Is the rotor turning? If not sounds like a timing belt problem-investigate further

Feb 19, 2013.