My cheap cross cutting shredder, which is a Chinese one (unbranded), made for B&Q 2006, has a mechanical plastic mechanism in the centre of the input slot, for sensing whether paper is in the slot or not. this tells the shredder to switch on when there's paper in it.
I expect your plastic mechanism, if similar to mine, is stuck somehow so that you can't see it and it thinks there's paper in it all the time. You could try unscrewing the casing (always unplug from mains first!), and vacuuming out all the dust which will have gathered there. Perhaps a fragment of paper has jammed the plastic mechanism so that it is not returning the switch to off.
Hope this helps.
piplewis57@googlemail.com, March 2008
