You have a grounded glow plug at cylinder #3. Remove plug and use a wire brush to get as much carbon out as you can, then crank engine with the glow plug out to blow out the loose carbon.
With series plugs, a ground somewhere it shouldn't be will cause the rest of the plugs to fail to heat, and it will both cause hard starts and burn out the rest of the plugs.
You may also want to pull the #3 injector and check to make sure the ball pin hasn't broken and fallen down in the pre-chamber -- this will both short the glowplug and cause serious injector knock. Requires removal of the pre-chamber to fix.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!