Could be anything. Take a sparkplug out, earth the tip against the engine block (with the plug lead on) and get someone to spin it over you should be able to see if you've got a spark, if not it is on the ignition side. Then just swap components over for new until it starts (that is what mechanics do*)
If you have got a spark then it could be fuel related, take all the plugs out and spin the engine over if fuel is getting through you'll be able to smell it under the bonnet, if not then start changing components over until it starts (it's what mechanics do*)
If the Cambelt has snapped then you aren't going to do any more damage than has already occurred (pistons only have to clobber the valves once to bend em)
basically it could be anything so trying to diagnose it over t'internet is a non starter (

) best to get a mechanic to look at it, I know it'll be expensive** but unless you know what you're doing you could be chasing your tail for ever.
* It helps if you've got a spares dept. full of all the relevant spare parts to grab and fit.
** with Main Dealers someone's gotta pay for the sharp suits and company cars that the 'managers' have whilst the guys who do the work get a pittance in comparison (sorry if this sounds a bit 'bitter' but I
wasted spent 6yrs as a mechanic at a 'Main Dealer' so I've seen it)