Recently, I've changed internet providers from Quest to Mediacom and haven't played my 3DS (or DS) since. Now that I have felt like a Pokemon mood, I pulled out Pokemon Black and connected it to my internet. Now that I try Pokemon Heart Gold to check up on the GTS, it doesn't seem to take my internet password. I don't know what's up.
Delete and then reestablish your Internet connection in the system settings. Is the system giving you an error code, and are you sure that the password is inputted correctly?
Okay. Turns out that none of my Pokemon games actually connect to the internet. Checked Diamond, then Platinum, Heart Gold again, and then double checked Black to see if it works. It turns out that Black never worked anyway. It told me to go to settings (I'm using my 3DS instead of my 1st gen DS if that helps) and choose Nintendo DS Connections. Once I scan for an access point from system settings instead of from a game, it doesn't even pick up my internet name and says, "The access point's security settings are not supported by the Nintendo DS. For help, visit support.nintendo.com" and the rest is history.
This means that your router has WPA encryption, which is not compatible with regular DS games. If you go to your router's settings, and then switch to WEP encryption, the 3DS will be able to use the connection for DS games.
Nintendo gives information on how to access the individual settings of routers. However, the closest router to your router that Nintendo gives information for is DPC2325. It does not sound like your router will be a very different version from DPC2325, so this information on router settings should help you even though the routers are slightly different.
I looked everywhere, and it looks like my router doesn't support WEP. The only way for it to work is for me to take out the internet password entirely which would not be a good idea. SONOFABISCUIT!!!! Aw well. Looks like I can only do this at an Internet Cafe or a library now or until I head to college next year. Thank you for your time, though.