Fully charged battery but my engine still won't turn

My 2.25 diesel won't turn over, it won't even beep the horn properly, I did think it would be the battery but it's not :s I've just changed the earth lead to the engine, when I turn the ignition key I just get a ticking noise from the starter

Starter solenoid/earth strap ?

Terminal not tight.poor connection.

Buggered starter and/or battery.

Is the battery in good nick? Even if you've charged it overnight it may not be holding charge - can you measure the voltage?
Do the headlights work? Do they dim when you try to start it? Lots of things can have gone wrong but most of them involve poor contacts - take apart, clean and remake all the connections then you can start considering buggered solenoid/starter.

hmm ill check the connections, the lights do go dim when trying to start

I had exactly the same problem, put another battery on an it turned straight over

new battery and a knock on the solenoid and away it went chug chug chug lol