Check the oil level. Engine may have seized due to lack of oil. It sorta depends on how long she's had it - did it have an oil leak?

You didn't say which model so I don't know if it would have an oil gauge or an idiot light. Some people may not focus too often on the oil gauge.

I really hope this is not the problem for you. Good Luck - keep us posted on what happened and what you find.

Ken
'82 300D
308k and counting