I purchased an aftermarket key fob and programmed in via their instructions (keyfobs.com) the key fob works fine but now my 2008 Mazda 3 wont start. every thing lights up as it should, fuel pump primes but when I press the clutch and turn the key... Nothing!!! Thoughts anyone?

 

It appears you have managed to only program the keyless entry. You now need to get the key programmed to the factory immobilizer, which can only be done by Mazda or some automotive locksmiths.

 

My key was working fine before this, also the key light on the dash does not blink indicating it doesn't recognize the key in the ignition.

 

Try your spare key?

 

I only have one key, I just purchased the car few months ago.