STB would be my guess ... I can't see any way a PC 'problem' could screw-up the STB, methinks the installer buggered the box installing the broadband bits and pieces ... sadly you're going to have to deal with Customer Service (sic).
Tip: DON'T report it as an internet fault to start with, if the TV's freezing report that, telling them you've got an internet problem is a recipe for being passed to some moron who'll have you going through the standard 'reboot the STB, now reboot the PC' rigamarole.
If it's the PC (which I doubt) you'll need to mention the internet problem, just don't be up-front about it ... when the internet link stops it's usual to find Interative Services also fail, they share a data feed, so report Interactive again instead of internet for as long as possible.
Good luck .. my prayers go with you.
Rob (an NTL BB user in Warrington).