Netgear's are generally reliable, Clive, but can be easily damaged by power surges or thunderstorms - the same is true for all routers.
A stale session is when the router is in sync, but can't create a PPP session because BT thinks that one already exists. The usual cure is to power off the router for 15-30 minutes. I can't ask support to look at what's happened at the weekend, but will do on Monday if the problem persists. Don't boot the router and computer at the same time, either leave the router on 24/7 or power it up and let it connect before you start the computer. Doing them simultaneously can result in the router being interrogated by Windows, and not being ready to respond.