How do i reset my imobiliser?

Hi, i have a peugeot 306 1.6 petrol 1999 v reg.
I removed and replaced fuses when my heaters stopped working. Now the engine wont start. I think the imobiliser may have reset itself. We dont have a imobiliser key pad. The only thing that comes on the dash is the battery light.
Please help. All fuses seem ok.