speedo

Well the sun has just popped out so thought i'd drag the bike out the garage.

All going well until I looked down - speedo reading zero (when moving) and miles not increasing.
Thought "bugger it" and kept going, everything else working fine.

Any suggestions on speedo prob.

Forgot to mention, yes the front wheel was on tarmac!!!

If I'm correct the speedo sensor measures the speed from the brake rotor bolts.
You didn't swap them with titanium ones?