iveco daily 35s9 wont start?

Anyone able to tell me what links my glow plug light on the dash board, to the vehicle not starting? it was left for 5 minutes in 20 degree sun, had run and started all day no problem. apart from the rev counter stopped working! got back in, switched ignition on, no glow plug light on dash board, engine turned over at good speed, but wouldn`t fire up. checked all fuses, and it started with cold start. got no spark when branched power accross to glow plugs directly, so not sure if there is a solenoid/relay issue. could it be an earth cable problem?
cheers, mark