I just upgraded my virgin box from the normal one to the HD package but my internet has been playing up ever since. It has an 'online' light on the box so was wondering if the box uses an internet connection as such which could answer this problem??
Had the same problem when I upgraded, they just sent me a new hub and that sorted it. Give them a call and they will run some tests over the phone and be able to diagnose the the problem straight away.