I had an issue with my drivers side seat.
There's a cable attached from the lever to the mechanism underneath the seat. You'll need to keep an eye on the underside of the seat and give the lever a few wiggles to identify it. Like a brake cable on a bicycle it should pull the seat mechanism up to allow it to slide.
Its a little awkward to explain in writing but here goes...hope you follow this....If you follow the cable route, you should see that it (the cable) is anchored to the seat infrastructure (on the underside of the seat, and towards the rear of the seat - nearest the car door)....and is anchored in place by a little black plastic hook.
In my case that black plastic hook had broken, I noticed this because the cable was hanging down loosely, however whilst its only a 0.49p part it was a bugger to fit...not impossible (i did it), but it was fiddly.
Hope this helps, but there may be other reasons why its not moving, this is just my experience.
