1990 190e 2.6 Not starting

I've searched the archives and tried everything that's been suggested but nothing works...... Here's the full story!

I've just replaced the head gasket on my 1990 190e 2.6 (U.K car). I lifted the head off complete with the entire inlet manifold and fuel injection system, and since putting it all back together, it just won't start!

I'm getting a good healthy spark on all the 6 cylinders, (firing in the right order and the timing is spot on as per the Haynes manual - checked by lining all the timing marks up - the one on the pulley at the end of the crank, the distributor (pointing to HT lead for cylinder 1) and the hole in the camshaft)

I'm getting fuel into each cylinder (plugs are wet)

The OVP relay is fine, as is the fuel pump relay.

All electrical connectors and vacuum connections appear sound and connected.

Any ideas what else might be wrong? Me and my dad have run out of ideas now! I've tried praying and kicking it.... lol

HELP!!!!!!!! I can't afford to take it down to the Merc dealers (let alone not actually being able to get it there!)!!!!!

Thanks in advance for any advice,

Martin