Try holding down the power button until it says "Stop" as this can sometimes make it progress further. If this doesn't work, it's dead and will need replacing.
Ring 150 from your Virgin landline or 0345 454 1111 from other phones and use the option for "if there's a fault with your TV service". It'll run some tests and then put you through to someone who can get a replacement box sent out. Bear in mind this will be a TiVo or V6 box as V+ HDs are no longer supplied.