Some Virgin Media customers were left without access to TV services for more than 10 hours, after the firm suffered a nationwide outage.
The issue began at about 10:30 GMT prompting thousands of viewers to report problems.
The firm told customers its engineers were trying to fix the problem, which hit cities across the UK, including London, Birmingham and Manchester.
Virgin Media apologised, and said it would fix it "as soon as possible".
The issue had been caused by "a major power outage", the firm said.
We’re aware of an issue currently affecting TV services and are working hard to resolve this as quickly as possible.— Virgin Media (@virginmedia) December 2, 2021
The website Downdetector which tracks outages received more than 18,000 reports of problems at one point.
Many users tweeted their annoyance at the loss of service, and the way in which Virgin Media communicated: "Can you update please? No TV. Your status page down. No info on phone lines," wrote one customer.
The company said it had identified the fault and its engineers were working flat-out to fix the issue.
At 13:45 GMT the company wrote: "We have now restored several channels with customers able to watch BBC One, BBC Two, ITV, ITV+1 and Channel 4. TV360 customers are also able to access apps on their box," the firm wrote.
"We're working to restore all channels as quickly as possible and continue to work towards having this resolved this afternoon."
But the partial return did not please everyone: "Channels 1 to 4 are working, but the problem is it's not the year 1985 and we pay for hundreds of channels," one customer tweeted.
And some users complained that the channels had appeared then disappeared.
The cause was revealed in a further update from the company at 15:30 GMT, "We are currently attempting to restore more channels. As we do this, it may mean customers temporarily lose access to previously restored channels.
"We recognise this is frustrating for customers and apologise again for the inconvenience caused."
At 20:15 GMT, Virgin Media said in a tweet it was continuing to restore TV channels with "many now back up".