If the service status for your area (accessed via the link at the top of the page) says no faults in your area, then ring 150 & report the fault. There may be a fault with your box, but more likely is a problem with the upstream (outgoing) signal from your box not reaching the network. In either case, an engineer visit would be needed to resolve the issue.
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV+), Talk Unlim Telco, VIVID 100, Virgin PAYG Mobile