This indicates a failing hard drive or faulty tuners and the box would need to be replaced in this case. Ring 150 from your landline or 0345 454 1111 from other phones and use the option for "if there's a fault with your TV service". You'll be put through to someone who can run some diagnostics and confirm what the issue is. They'll either send out an engineer or post you a new box.
Let us know how you get on.