You might want to drain your old fuel like oldsinner111 suggests. I know you've got diesel not petrol but it has been sitting for quite a while. There might be water in your tank - who knows?
I've added some information to the picture you posted to help you out.
Next time you'll probably get a quicker response if you post in the diesel section of the forum
Diesel Discussion - PeachParts Mercedes ShopForum
Perhaps a moderator can move it for you (if you want).
The first thing I'd do is undo the line on the primary filter and make sure it is diesel going through the pipe!
Then use the hand pump to bleed the system
Then give it another whirl!