It sounds as though either the router's WiFi has become switched "off", or it isn't broadcasting its SSID so that network adapters can find it.
Can you go into the router's wireless settings and check that both of these features are enabled? Type the router's IP address (192.168.0.1) into your web browser and then, when prompted, the Username & Password. The Username is selected as either User or Admin from a drop down menu, select Admin. The default Password is either left blank or "Admin".
"Neither can my HTC Desire phone..."
There is a useful little Android App called WiFi Analyzer which lets you see the networks that are broadcasting and their signal strengths.