Crank shaft not turning when engine is running

If the engine is running, the crankshaft IS turning. The engine cannot run without the crankshaft turning. The crankshaft is what the connecting rods to the piston ride on. No crankshaft, no engine running. The crankshaft pulley may not be turning if your harmonic balancer is separated. I would think, though, that another one of your pulleys is locked up. Remove the belt, inspect all pulleys for free play and wear.