I recently had a similar problem after shutting everything down and going away for a few days.
I disconnected everything, connected the desktop PC to the modem and could access the internet. I then ran the Belkin router setup software, following the instructions to connect cables as prompted and bingo, all was well again. The weird thing was that after doing this the router had retained my WEP settings etc.
It may be worth a go - 10 minutes maximum.