Reprogram ford key fob!!?

Hi, the other day i bought a focus and remote locking was not working so i tried to reprogram useing internet instructions but nothing happened, so i tried a mondeo key that was the same type and the remote access worked but the key wouldn't start the car, which i then found out the reason for this is the key fob is linked to the car as well. So i put it all back as it was and now i can't get the mondeo key to work like it did before!! Ive tried the same internet instructions but none of these work!! Has anyone got any other ideas please?