1998 r reg megane immobiliser problem?

hi can anyone help me fix my 1998 r reg megane, i parked it up one night and following morning came to unlock doors via key plip and it would not unlock, i unlocked it manually and the alarm triggered off, i tried starting it and it would start for a split second and cut off, can anyone help me as am a home carer and unable to get to work, i have to ask my boyfriend to drive me around, any help would be appreciated my chassis number is VF1EA0F0G16530101 THANKYOU