Reboot it. If you feel like it, note what state the router is in first (wifi on, can ssh in, etc.). RECORD WHAT YOU DO in the Technical Logs.
If there are many networks using the same wifi channel, it can make it tough for people to see and/or use ours. Use a stumbler (iStumbler or MacStumbler for Mac, NetStumbler or one of many others for Windows) to see what other networks are around, and note which channels they're on. Generally it's best to only use channels 1, 6 and 11. If the router's current channel is used by many other networks (or if the wifi signal might be receiving interference from other devices, like a cordless phone or microwave), try switching it to another channel. To do that, ssh in to the router, and issue the command (to change to channel 1):
nvram set wl0_channel=1
Then (to save the change to the router's memory):
nvram commit
Then (for the change to take effect):
reboot