Right, simple, if you get an ip address.
Start, Run, cmd, then type ipconfig /all
Note the default gateway, could be 192.168.1.1 for this example.
Now go to internet explorer, type 192.168.1.1 press enter.
log into router, most people its admin and password.
Go to status, see if it is connected, then go to maintenance, do a ping from there to say google.co.uk.
Failing that, go to the router, disconnect the cable, plug the modem straight into the laptop, reboot modem, then reboot laptop to get a valid ip.
Try getting on the new with that.
Rules out the router. If you can get net via the modem on its own then Phone Virgin Media to resolve it.