1977 240d turns over but won't start.

[Vonny]

Ok, I am a novice with diesel and mercedes-benz vehicles. I recently bought my first MB, a 1977 240D (automatic), and decided that I enjoyed it enough that I wanted to keep it alive. From my point of view it ran well enough. I had no trouble from the vehicle until the weather turned cold. The winter last year was a bit more extreme than we are used to in my part of the country(western ky). For about a week it was horribly cold for the area, reaching 20ish below for a few days. i knew it was coming so i filled up the tank and put some diesel additive in to keep it from freezing up. After that, the car wouldn't start and apparently the block heater went out. It does turn over, but it doesn't start. So, I tried jumping it, replacing the fuel filters, and changing the glow plugs. After all that, I bled the fuel system. Then I decided to get a new battery, still nothing. With my meager knowledge, I have no clue how to fix this car. I am not sure if the block heater going out and it not igniting are linked. I checked the fuses, I looked at the relays, but I am not sure what a bad relay looks like. The starter is new as is the alternator. I am at the point that the car will be sold or fixed by a mechanic if I can find one that knows these cars. Any ideas or places to start would be very appreciated.