There's a limited number of things that could be wrong with it:
No air.
No fuel.
No compression
No heat
All there but not happening at the right time

Looks like you have heat so chase down the others.

Many forum members have discovered in the case of Mercedes diesels that have sat for a long time, that pull starting is the most effective means of reanimating them.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13