Have you recently installed or moved a cordless phone? They can interfere with Wi-fi as they use similar frequencies. Phone base station near wifi point caused trouble for me.

Other possibilities include:
* new Wifi installations in neighbouring buildings
* your Belkin is dying.
* someone moved the antenna slightly. Really! - I bought a new wi-fi access point because my first one had never worked well, but then I changed the antenna orientation from vertical to 45 degrees off, and everything sprang to life and worked so well I never installed the replacement.

Anahata