Howdy Smileytammy,
Thank you for coming in and posting, welcome to your Virgin Media Community 
I'm sorry to see that the box has been turning itself off on its own, this can happen if the box is left on but not used after more than a few hours.
How long are you seeing this happen after running time?
Also, I've been trying to access your account to look into this more but have been unsuccessful, can you have a check in your 'Inbox', as I've sent you a 'Private Message', you can find this by clicking on the little purple envelope near the top right of the page.
Speak to you again soon.
Ben