Immobiliser fault
 

Evening lads and ladies, I'm new to scoobynet and have some questions. Wonder if anyone could help me, I have a uk2000 99plate Impreza wagon with I think a m30 sigma alarm system. Bit of back story, the car has been off the road a couple months due to money being too tight and needing new battery and maf sensor. Since then I have fitted nice shiney new bits and try to start the car. The fob won't seem to connect to the immobiliser at all. No matter how many times I press the button. Usually when this used to happen I'd press the button 5-10 times next to the code box and it would work fine again. However recently it's just having none of it! I don't know the immobiliser code either which is super helpful. Also when I went to Subaru they were absolutely useless in finding a code. Any help would be hugely appreciated:)
Thanks.