OK first off do you have the 'sync' and 'ready' lights lit on the modem. They should be solid and not flashing.
If they are not solid you need a tech to put it right. It will be because your signal is -21.6 db. It shouldn't be below -10 really.
If they are locked then you need to hook the computer up directly to the modem and forget the router for a while.
With it connected go to your web browser and type in ' activation.virginmedia.com ' OR '
https://autoreg.autoregister.net ' and follow the on screen activation instruction.
You do not need a CD but you do need a pin number which you should have either from a letter or the install tech.