No go crossflow

Fitted a new battery yesterday, turned the ignation key, and........nothing. Lights working, petrol pump chattering away, instruments dead, instrument fuse is ok, started ok beginning of the year for a warm-up in the garage. Car's a crossflow and it's obviously an electrical problem, but I'm not a mechanic, so any ideas where the fault might be before I start poking around and make it worse?

Well.....success! The immobiliser is an Autowatch, so I googled it and it turned out to be an easy fix. I'd never have thought of it being the problem so thanks for the suggestion BertBert.