This afternoon, rather unhelpfully, my wireless connection suddenly died. No amount of rebooting, either of the router or PC, was making any difference. The poor little access point was simply not picking any network up.
Finally I hit on the answer. By changing the frequency from the default channel 11 to 5, everything suddenly boomed into life again. I suppose something must have happened to cause interference, but it’s very weird. I can’t detect any other wireless networks operating nearby. There was a heated political argument going on earlier, does politics operate from 2449.5 MHz to 2474.5 MHz by any chance? 
