That sounds like an issue with your router, but it could be the computer you're connecting with. How many computers have you tried to connect with? If only one, could you test with another system? Have you been able to connect to other wireless networks with your test machine(s)? Again, we just want to eliminate the client as the problem before turning to the router.
Next, when you can't see the wireless network, try a wifi enumeration tool like NetStumbler. It won't debug connection problems, but it will let you verify if the network is being seen at all.
Finally, update / reinstall the router firmware via the admin panel. This probably won't help but is worth a shot.
If none of these work it sounds like a physical defect, possibly due to electrical damage from a storm.