If the LED next to the painted heart symbol is flashing, there's your problem.
This is the status for the onboard internet connection, and flashing means "offline". No internet connection means no OnDemand.
It's a fault, so treat it as such. You can either call in (150 from VM, 0345 4541111 otherwise) but I'd recommend being clear that "My heartbeat light is flashing". Or wait here a couple of days and VM staff should respond.
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