I've recently bought a new handset and "please check the line cord" is appearing, I've tried the handset on another line and it seems to be working fine! I've googled the problem and seems to look like other Virgin media users have had this problem.
I'd like to take this opportunity to welcome you to the forums and say that I'm really sorry to read that you are currently experiencing an issue with your phone line, and I'd like to help you out.
Thank you for letting me know that you've tried your phone on another line, as this really helps. Testing on the line hasn't shown up any obvious issues which would cause this fault, so I'd now like to look towards booking a technician to call out and investigate further for you.
I'll send you a private message in order to get things moving, please look to the top right of this page where you'll see a purple envelope icon, click on that and you'll see my message.