NO DON'T TRY THAT!!! It's the worst thing you could do with the belt in an unknown condition.
does the engine turn over with the key if so then it isnt seized.
You need to take out the top torx bolt holding the cambelt cowver on and push down on the belt (if it's still there) any movement and it's shot, if it's not there then you know what's happened, head off / sump off and cry time if it's on there still then raise the car and whip off the aux belt and timing covers and check the tensioner position (the arrow should be pointing at the hole), It's unlikely but the cam may have jumped a tooth and in which case the engine will shut down. Either way factor in £500+ for parts.
If your lucky the crank sensor has just failed, this will also cut the engine, it would though start again once cooled down normally as it sounds like this is the first time it's happened and it's unusual for them to just completely die. Also just to make sure the connections fine, on the timing side of the head is a brown plug, just disconnect it then plug it back in, it may then work. £35 if it's the CPS. Rear engine mount off for access.
if your less lucky then the cam sensor just died, this would be best done along with a belt change, you need to lock the cams anyway and remove the pulley to do the change so factor in £400 for parts on that one.
Those are the 3 things that will do this and unfortunaetly for you I've listed them in the most probable order, but above all, check the belt first as turning the key will cost you £1500 if the belt's snapped.