Do you have another key that you can try, as it may be a defective transponder.
If you have an adjustable steering column, give it a wiggle incase it is the reader coil.
Try disconnecting the battery + and then reattach it.
Alternatively, with a fully charged battery 12.5v, try turning the ignition on (dont start the engine) and leave it for 15mins. Then try and start the engine again.
Do you have an aftermarket immob/alarm fitted?
Which factory immob do you have, immob 2 or 3?