Re: set top box saying no signal error 7400, but all other 3 boxes working.
I'm sorry you are having issues. It's doing that because the box hasn't been activated yet. Have you followed the advice here? virgin-tv-error-codes/7400
If following the instructions on the above link don't work then you need to call 0800 953 9500 to activate the box. You will need the box serial number, and your account number and area code.
You could also try contacting New accounts and Set Up for them to complete the setup and activation. That would be options 1,1,1 and 4 if dialling 150 from a Virgin landline , or options 1,1,2 and 4 if dialling 0345 4541111 from any other phone
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