Do you get 12v to the starter motor? If you do whack the solenoid and the main body of the starter motor with something enough to shock it. The fault maybe due to something sticking inside.
On the other hand, if you are not getting 12v to the starter, check your fuses and it may be possible that your ignition switch or immobiliser is faulty.
On my 16v, the rev counter used to jump when the hall sender of the dizzy was playing up, i don't know if this applies to your situation though. Could be possible the voltage going to the stater which isn't consuming it, is making other units play around. (that was an un-educated guess!)