Changed thermostat and now won't start

Yes there was a ground on one of the goosneck bolts and it was reattached. The only other connections were on the air intake (two) and they were reattached. A small amount of coolant was spilt but only on the radiator side. I'm not aware that anything hit the alternator and if so probably not hard enough to cause any damage.

I thought so too and I did give it a boost but no change...1 click and that was it. Had the battery checked and it is fine. As I said, it started perfectly prior to this.

Guys, I really appreciate the responses and being new I don't want this to sound wrong but none of these would have changed just because I changed the thermostat. The van started perfectly immediately before the replacement but will not start immediately after. I am not getting a clicking sound as one would expect from a dead or low battery. All I am is getting a single click from what I am guessing is the solenoid on the starter and then nothing. I am open to suggestions but I have checked all of the obvious issues. Thanks.

Astro355 turns out you're a genius. My son did most of the work on it and apparently he dropped a bolt back there. It seems that is wasn't arcing but just creating a direct ground to the block.Pulled it out of there and it fired right up...perhaps stronger than before. I want to thank everyone that responded. It's nice to know that there are people willing to help.