81 300sd

been sitting parked for maybe 3 days, went to start it up today and the starter made a really bad sounding grinding noise (never done that before)

tried to start it again and did the same grinding

tried a third, 4th , 5th, etc and now its just clicking.

tried to turn the crankshaft bolt by hand and pushed as hard as i could, it wont budge.

this is my daily driver. what possibly could have happened to cause this?! i havent touched it since i parked it.

http://www.youtube.com/watch?v=aae0rf76PyI

__________________
1981 300SD, 270K, two tank wvo system
1985 300D, 288K, california version
1985 300DT wagon, 315k, broken odo