Then it's dead. Just to make sure, switch it off and switch it back on whilst looking at the front of the box, usually you'll see the blue ring flash briefly. If it does, press and hold the power button until it says "Stop" as this can force it to boot up. They can sometimes take hours to boot.
If you're having no luck, call 150 or 0345 454 1111 and use the option for "if there's a fault with your TV service". They'll either post you a new box out or send an engineer. Bear in mind V+ boxes are no longer supplied so you'll get a TiVo or V6.
Don't bother opening it as that's against the T&Cs of your contract + if a fuse has blown then it's done so for a reason and replacing it would probably just cause it to blow again.