Check the front-left of your box, there's a series of green lights. Second from left is your "online" light which indicates your box's internet connection.
Solidly on is good, flashing is bad. If that's happening, I'd suggest calling Virgin on 150 to report the fault.
If you have Virgin broadband and also use the streaming apps on your box a lot, I'd recommend taking a look at the newer V6 box which handles them all a lot better.
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