1. Check the router management page (from a browser on a wired desktop) if maybe the wireless has been disabled for some reason.
2. If nothing strange appears there (compared with when you had your last look when it still worked) it's time to buy a new router.
My Dell computer uses a Belkin G router (one of the older models) to offer a secure connection to two laptops, two desktop computers, and a handful of handheld electronics. We haven't had many issues with it, but when we got back from a three day vacation, both the lights for 'wireless' and 'secure' had been turned off and the wireless isn't working, even after three more days. The internet on our main desktop computer is still working, though. I've tried holding the reset button, then unplugging it from everything, waiting 10 seconds after the lights went out, and plugging it back in. Nothing's worked. The 'wired', 'router', 'modem', and 'internet' lights are still lit and working. On our Motorola Modem, everything is green, too. I really need help with this, but please use layman's terms, for I'm not very computer literate.