Usual problem with the 968 tip is that full auto mode works but manual does not - caused by the actuator arm on the relevant microswitch breaking - I've had that on both my 968 tips! Remove the gear knob (unscrew the centre button then straight pull the knob off, mind your face as it can be tight) then carefully prise the gearstick surround off to expose the selector plate underneath. The manual select microswitch is in the drivers side centre of the plate, if the actuator arm is broken it will be obvious, and you will be cursing as replacement part is either very hard to find (the actuator arm removes/replaces easily IF you can find a replacement microswitch) or is NLA, even from the original manufacturer. I think you can still get the complete selector plate from Porsche, but probably over £200, and "interesting" to fit because of the cable connection to the ignition switch that stops you removing the key unless the transmission is in P.
There's quite a lot of info about this on the Porsche968uk forum, which as a 968 owner I would recommend you join.
If this is not your problem, then it would seem the transmission is stuck in "get you home" or limp mode, explained in the owners manual.
