The first port of call with any P38 is to lift the main fuse box cover and look at the main battery terminal (wriggle it and listen for crunchy noises) and the relays and fuses. Once you've identified the starter relay check it's input voltage at terminal 30, bridge 30 to 87 and see if it cranks. 85 should be input from the key and 86 should be the earth path via security and inhibit switches.