reset or bybass immobiliser for petrol peurgeot 306 1998?

please help just bought peugeot 306 it was sat outside for 2 days went to go out in it and battery was dead, charged it up, went and put it back in and it would not start, again battery gone flat, nothing is working, no lights,no clock and key not responding to central locking. was told it is the immobiliser need to fix this a.s.p as start new job out of city on mon day pleeese someone help me