First of all, let me say "I'm no expert". Maybe you'll get some more experienced advice than mine.

If it were mine, I'd go as far as removing the valve cover to check the timing chain and valve train first. This will tell you if the timing chain is broken or slipped (not all that likely, but if it is broken and you crank it over - bent valve - of course it may already be bent).

Next I would suggest trying to turn the engine over using a big socket on the crankshaft. Easier said than done. But the idea is to see and feel how the crank turns and if there is any rattling sound (very bad news - maybe broken rod - not likely) You can also watch the valve train while doing this.

If it were non-running I'd adjust the valves while the valve cover was off. Then I'd bump the starter for a few revolutions. Everything seems OK then back on with the valve cover.

Next I'd try to start. If no go I'd check the fuel supply by loosening a pipe near the injector and crank. No leakage, its not getting fuel. Blockage?

Next thing to check would be glow plugs.

When you know you're getting fuel and glow plug operation, it cranks OK and sounds OK but still doesn't start, then it may be time to test compression.

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You could shortcut this a little and just check fuel delivery and glow plugs. Probably a more likely culprit than broken timing chain or piston rod. And like TD said, glow plugs are very likely to be the problem.

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Once you get it started then its time to change all fluids and filters.

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Did I mention I'm no expert? Let us know what you find so we can add it to the mental statistics of "what can go wrong".

Ken300D