We've been having a strange issue with my brother in-law's laptop. We have 2 separate wireless networks in our house, but his laptop will only "see" one of them. All other devices like phones and other laptops can connect to both networks without a problem.
There's no mac filtering set on the router, we've tried resetting the router, tried manually connecting to the network, but it wont at all... I know it's not a driver issue because it can connect to the other network just fine.
Any suggestions?

Are you sure both access points are broadcasting their SSID's? That can be disabled so a network is invisible. He should be able to connect to the "invisible" network via its SSID explicitly. Once he does so, his system should be able to remember and see it in the future.

It's broadcasting because we can see both network (A) and (B) with phones and other laptops. Also, I've checked all the settings in the router, and the SSID is broadcasting. We've also tried connecting manually to the network by typing in the SSID and it still wouldn't connect.

Check the settings (properties) of the wireless adapter on the computer. Ensure that it is set to use your router is using (a/b/g...etc).

Good idea. I'll try that this afternoon and report back

Checked the settings, and it says it's able to connect to a/b/g/n networks. The router is an N router (same as the other networks we can connect to) His wireless adapter also says it's compatible with 5.2ghz N and 2.4ghz N networks... I also checked his router settings and it's set for mixed b/g/n... I'm really stumped on this one.