If you look at the speedo closely you will see a "stopper" pin that prevents the needle dropping any lower than 10mph so it will never show lower than that even when stopped.
As for it not going above 10mph, does your rev counter work at all? If no, then there is a fuse in the fusebox that has porbably blown so check that. If the rev counter is working then you need to check the electrical connections for the speedo.
The speedo pickup connection is located on the bell housing at the back of the gearbox so I suggest you check that it's still plugged in and isn't loose or snapped off. To get at it you will need to remove the air intake pipe that goes between the airbox and the throttle body. See the pictures in the following thread...
If that looks fine then check the electrical connection on the back of the instrument cluster and re-seat it (unplug and replug) to confirm that it's plugged in properly.
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