Modus DCi 80 non starter new battery immobiliser light always on.. Help!

Hi all..... My Modus DCi 80 2005 is a non starter... Battery went flat a couple of months ago... As I was skint I left it in the garage until now... Just put a new battery on, the correct battery & it won't turn over at all, just the relays clicking... Key remote control opens & closes doors all ignition lights seem on & ok, immobilizer light doesn't go out.... Any ideas I would be most grateful to receive.... Many thanks