Help! Diesel won't start and key won't turn.

I am the proud owner of a '72 220D that was purchased new by my grandparents. The car runs great and is a pleasure, but lately with the newly cold weather, it's been quite a challenge to start. My father seems to think it's related to the fuel injection system or the fuel pump. Does that sound about right? Also, starting today, the key won't turn in the ignition to power the car so I can start it. (Everything's right; it's in park, etc.) Any answers or suggestions would be appreciated. Also, there is a '67 250SL (silver, navy blue hardtop) for sale in my family if anyone has any interest.