Immobiliser problem 94' MK3 Golf GTI 2lt 8vl?

I own a 94' Mk3 Golf GTI, which has been stood for few months and battery has now gone flat. After charging the battery, I've found that the Remote Central Locking will not open the car, or turn off the Immobiliser or alarm. Central locking works with Key, but the engine will not start because the immobiliser is de-activated only with the Key Fob. I've replaced the batteris in the Key Fob / remote, and it appears to work, but the car just will not register anything from Fob...

I want to sell the car for parts, but cannot prove the engine works until I sort out the Immobiliser.

How can I find the immobiliser and fix it, or just by-pass it to get engine started??

Hope someone can help me..... Thanks!