i havnt got a spare key, just the key fob with infar red with a key that slides out of the side of the fob
I was afraid of this. I'm reluctant trying to help owners that do not care to keep two active keys for the car but you probably have a good reason for this.
I assume the key does not turn in the ignition slot? Then it sounds like an EIS or key issue. You could check if the key emits an IR signal (take a photo with a digital camera when you press a key).
In the ignition slot the key does not need batteries but when you test it, batteries need to be correctly placed.
If you do get an IR signal, I'd open the key, take the circuit board out and check that the power coil is in place, switches and other solder points are fine.
But if the car has power but doors do not open with the remote, it sounds like a more serious issue with the key. At this point either the RF or the IR part would be sufficient, so I cannot figure out a common problem.
If the key turns in the ignition slot, then it is something different, in this case the car has authenticated the key.