Any box that keeps rebooting generally needs replacing.
It probably won't remedy the issue but have you tried a factory reset?
To factory reset go to Settings (the cog at the end of the Home menu) > System > Factory Reset. It's actually misnamed and only a partial system reset and not a complete factory reset. You are given 2 options
Keep Recordings
Format Disk
Choose Keep Recordings, that means you won't lose your recordings and any planned recordings or series links you've set up. You will have to sign into your apps such as iPlayer, Prime, Netflix and ITVX again. Also Match frame rate and Standby power consumption will go back to their default settings if you have changed them.
If that doesn't work then you should call 150 from a Virgin landline, or 0345 454 1111 from any other phone and select option 2 (Faults)
When calling Faults ignore all the options and don't press any buttons then you should be placed into a queue and an agent should pick up the phone and book the tech for you.
Or wait a day or two and a member of the Forum Team should pick this up for you and arrange a tech visit.