Hello and welcome to JustAnswer!
If the engine died with a thud and now will not crank then it sounds like something is preventing the engine from turning.
I'm assuming that everything electrical still comes up and works? Do you hear a click when trying to crank the engine?
The first thing I would do is take a look at the front of the engine and make sure the belt is intact and nothing foreign is stopping the engine from turning externally.
I would also recommend checking the oil, if the oil had ran low enough it could have caused internal engine damage.
If you don't see anything externally then the next thing I would recommend is using a socket and ratchet on the crank damper bolt and see if you are able to turn the engine, from your description I don't think you will be able to. If not then it's possible that the problem is in the transmission but it's most likely an internal engine failure.
If the engine does in fact turn by hand then internal damage shouldn't be an issue, but the fact that it died with a thud and now won't crank leads me to believe that the engine may not turn.