Mk111 turbo won't start

[El Supracabras]

If its a non turbo, you could try taking out the distributor and turning it. I actually had this happen to me, the distributor seized in an 86.5 n/a and the engine would not crank.
If you cant turn the engine with a breaker bar, I'd bet that it is seized. You can try diesel but chances are it's gonna be hurt even if it frees up. It aint no Chevy! If you were planning an engine build, now would be a great time.
EDIT- Also had this happen (on a camaro). It turned out that a couple mice had chewed through my air filter, crawled in through the intake all the way into the cylinders and completely filled a couple cylinders with corn kernels. Where the hell they got all that corn, I still dont know (I live in Chicago!). They had quite a stash in there, enough to prevent the engine from turning. When I started pulling the spark plugs, corn was pouring out of the holes. They had also chewed through a bunch of wiring under the hood. The car was only sitting for a year.