Sounds like something new nearby may be interfering then, may be worth scanning with
http://www.metageek.net/products/inssider/ - but unless you use a more expensive product with a dedicated receiver, most scanners that use Wifi hardware can only scan for Wifi signal strength, a few Wifi devices can report noise level, though not necessarily in a useful way (eg. my Ralink chipset one, which gives a noise level indication in the connection stats, but no use in diagnosing a no connection issue!).
And finally, almost any electrical/electronic devices can generate interference, so it's usually recommended to space the router away from any other electronics.
Anything at all changed recently? even if it's not a device that's meant to do anything on those frequencies, because if all channels are bad, it seems possible that it's a source of wideband, incidental interference, rather than something generating a precise signal - or somewhere nearby, there are 4 videosenders hogging each of their 4 channels that they split the band into.