A couple more things to check, sorry if I'm teaching egg-sucking.
1. Are all the fuses ok?
2. Is there a battery isolation switch (big red key thingy) which has got inadvertently knocked around to the off position?
3. Are the battery clamps nice and clean and tight?
My money is still on the battery earth strap - if it was the engine earth strap then you'd expect the dash lights to work but the engine not to start.
