I did a self install of a V6 yesterday and encountered that 7400 code during the process. However it cleared after the final restart following several firmware updates.
_________________________________________________________ Graham I am a VM customer. There are no guarantees that my advice will work. To say thanks click the kudos thumb. If I have solved your problem please click the helpful answer button.
Firstly I'd like to welcome you to the forums and say that I'm sorry to hear that you experienced issues setting up your V6. I hope all is working for you now, and that you were able to watch some of the Rugby over the weekend.
I've run some testing from here to see if I can detect any issues, and I'm unable to communicate with the V6, this could be that it's powered off, or that there is an issue.
Should you still be experiencing this issue, could you please power off the V6 for about 30 seconds, then power it back on, allowing up to 30 minutes for it to fully load, should you still be experiencing a fault at that point, could you please let me know - and leave the box powered on so that I can run any testing.