I bought a replacement case for my car key and mid way through changing the case someone came to my door, after finishing putting my key back together, it won't unlock my car. The light flashes but won't unlock. I've tried all the YouTube videos I can find but no luck. Also there's an alarm that keeps going off and when trying to start the car it tries to start then cuts off. I assume it has an immobiliser and I still can't get the key to resync. Are there any other methods I've not tried? Please help.

07 car, so you got the same key as me.

 

Make 100% sure the batterys in correctly. The LED will still flash even if battery is not installed correctly, start there, i had this after i lost keys and had to have new keys made, they refused to open the car, then one day i stuck new batterys in desperation and they worked a charm after they, they shouldnt need re-syncing.

You can see if they need re-sync by starting the car, it will say SAFE in the clock if the key is not presenting valid data to the barrel

It does say safe on the clock, I'm following the videos precisely but no use. 

press and hold lock button on key, put in car and ONLY turn to egnition for 5 sec then remove. prblem should be fixed. i had to do it a few months ago and it worked fine;)