If your speedo doesn't give a reading at all, then check the following:
Check speed sensor
Check the speed sensor (1) above the rear axle of the vehicle.
There should be a 0.8mm to 1mm gap between the sensor and the cam wheel.
Adjust the speed sensor if necessary.
Check all the wiring at the rear of the gauge.
To access the speedo from the back, open up the bonnet to access the rear of the dashboard.
Check wires are all plugged in and in order. Use the codes on the wires, against the chart below to match their location on the dashboard. (You can also download this chart below).