Help needed with rev counter and speedo?

My speedo and rev counter do not work, vehicle is an 'N' reg ex council welfare minibus. The 'test' function works ok but no rev counter or speedo when driving. Anyone got any ideas? Also today, whilst doing about 50mph the cam belt snapped does anyone know if this is a big job - is it likely to have bent the valves? any idea of cost to fix? Thanks for anyone who can help !!