I tried to changed the radio and as the new radio didn't fit I put the original back in, I done this without disconnecting the battery 🙊 the radio asked for code and I put that in but now the car wont start, no ticking over noise, when i turn the key the immobiliser light comes on solid then flashe's like mad then goes off, anyone got any idea what wrong, when I purchased the car I only got one key with it, car is a fiesta mk6 2002 zetec model, the radio is a 4500 rds e.o.n triple deck radio, help please?? 

Edited June 18, 20169 yr by Jennifer1985
Spelling mistake

Have you tried disconnecting the radio again to see if the car will now start?

could also try disconnecting the battery for 10 minutes to see if that clears the problem