‘02 Blown engine?

Just replaced battery after the old one died, suddenly starter makes a loud bang every time I start (this had happened maybe once or twice before). Today after starting it runs for 5 seconds then there’s a loud bang from the engine and it dies.
Is the engine blown? Didn’t try starting it again in fear of making it worse...
I noticed the coolant reservoir is almost empty. I have never noticed any leaks and engine temperature gauge has NEVER moved from normal temperature. Oil looks fine. Belts look fine.
Should I try starting again or just have it towed to mechanic?

 

I would not try starting it again until you find out what is wrong. My guess is it leaked coolant into the cylinder and hydro locked. Best of luck to you, let us know what you find out please.

 

Check the fluids. Pull the oil dipstick. Any milkiness to it? If so, it's not looking good. If not, then probably no coolant in the oil and that's good.

Open the radiator cap (always when COLD). What's the level like there? If it's near the top, then probably it was just a little low. The coolant reservoir level means little.

It could be the starter went south and its throw-out gear got caught up in the ring gear of the engine. That would explain the "bangs" and the ultimate seizing of the engine.

Next step would be to remove the starter and inspect. Then get a breaker bar on the crank bolt and rotate back and forth and see if the engine frees up. If you are SUPER SUPER lucky...the ring gear hasn't been damaged enough. Then replace the starter. BUY ONLY A TOYOTA STARTER!

I'm betting someone swapped in a cheap Chinese starter that lunched your engine.

 

Checked the oil dipstick and the cap and there's no sign of coolant...
I checked the radiator cap and there was only a little bit of coolant at the bottom... I'm not sure how far up it should go, up to the cap? The reservoir was almost below the Low mark...
I checked the timing belt and it's intact. Also checked battery cables had no voltage drop.
Didn't get the starter out, that seems like a lot of work... I rely on the car to get to work so looks like I won't have time to do this myself and will have to take it to the shop tomorrow morning... I might try turning the crank bolt first, if it turns, is it safe to try starting it up or should it be towed?

 

Take it to the shop. Do not start it. You have a very large possibility of making a repairable situation worse.