Hi all!

I have an NA V6 that up until recently ran completely fine. The battery was in desperate need of replacement so I went out and bought a new one, swapped it over and that's when the issues began.
The car absolutely refuses to start now.
All interior/dash/head and tail lights are still functioning and the radio is still working fine, it just simply won't turn over.

I contacted someone to come and have a look at it, he said it was the Immobiliser causing the issue.
He went on to unbolt the Immobiliser, cut all the wires connected to it and then "went to lunch".
I haven't seen him since.

I'm hoping I can fix this problem myself as I'm done with having random people coming to work on my car if I don't know them, especially after this incident that cost me $150 just for him to show up.
Any ideas or help would be hugely appreciated.