I have just plugged I my TiVo box today and every channel has an error message 7400 on the screen
Welcome to the community and thanks for posting. I'm so sorry to hear you're getting the error message 7400 on every channel. It sounds like the signals haven't quite reached the box.
I've managed to locate your account to run some tests. I can see the TiVo® box is showing as online. Can you confirm if the error message has disappeared?
Please let me know if you have any further issues and I'll happily help.