Is your fuel gauge also not working?
Do your instrument lights work?
First thing I'd do is check the fuse.
Then clean your ground points... There's a main ground header under the bonnet, next to the overflow tank. I believe it's gray.
Next I'd check to see if the speedo is getting power.
ignition feed - white green (position 10 on the back of the speedo plug. one w/more wires)
transducer feed - black red (position 2)
from ecu - yellow pink (position 1)
Cheers,
Jabber