Hydro locked?

I bought a '92 Previa last week, and even though I checked the coolant reservoir, which was low, but not empty the tailpipe, etc, it turns out that it's got a bad head gasket. Two days ago, it started running rough on start up, and I then saw the dreaded white smoke from the tailpipe. I looked in the coolant reservoir, and it was pretty much empty after only having driven the van about 100 miles, so I filled it to the full line. I didn't drive it yesterday, and when I went to start it this morning, it wouldn't turn over. I turned the key, and it made kind of a "clank" sound.
Am I experiencing hydro lock? Any other ideas? Thanks!

I was just outside looking at the van, and there's a small amount of coolant that's leaked from the exhaust in front of the catalytic converter.

With the cooling system located essentially above the engine it's quite possible a bad head gasket could have allowed enough coolant in to hydro lock it. Don't try to crank the engine any more until you get the coolant out. My brother recently went through this on a chevy v8 and the half a revolution or so was enough to bend a connecting rod. You'll need to pull the spark plugs to get it out and then just bump the starter to begin with or turn the engine by hand. Make sure you're not in the line of fire as the fluid clan shoot out with significant pressure. Also check the oil dipstick for any sign of coolant in there. At this point it's not likely to be milkshake consistency but may show as overcooked since the oil would be floating on the coolant.

Has anybody tried the Bar's Leak head gasket fix? It gets pretty good reviews online.

Don't even bother unless you're going to sell the van to the next poor soul...

the "miracle fix in a bottle" usually makes things worse by clogging up the heater core or radiator... if that stuff worked, dealers will be using them to fix late model cars with head gasket issues under warranty, but they don't because it's a corner that can't be cut
the only fix is to replace the engine or replace the head gasket... I understand it's a lot of work, but it's the only true fix