Grief, what a lot of emotions poured out there!!!
It is very unlikely your router could have damaged your computer and corrupted/lost its drivers on its own.
We'll need to go through this methodically ~ please help by telling us the sequence of events, plus whether all of your PCs have Windows XP.
1) NTL broadband ~ is this a standalone modem or a set-top box?
I hear set-top boxes have more problems ~ my NTL standalone modem has never been any trouble for > 5 years.
If there are now problems with a PC connected directly to NTL’s broadband kit, but without a router nor wirelessly connected PCs, then these problems have nothing to do with the router nor wireless settings ~ it is just coincidental.
Get your standard (non wireless) broadband and PC setup working again first.
Some other activity has probably corrupted your PC’s setups and drivers.
No point moving on to sort out the wireless aspects until your standard broadband setup is working again.
2) When you say things “goes offline every couple of hours ~ for days or weeks”, this could be down to the NTL box and/or router box overheating.
Are they positioned so that they have plenty of space for free air-flow?
3) Faulty kit; it could be possible that the NTL or Belkin boxes have a fault or have developed a fault.
NTL will test and replace their kit.
Belkin has a lifetime warranty if you still have the receipt.
Hope that has been of some help in all your frustrations after months of attempts to sort this out.