For some reason, any computers that are connected via a cord cannot access the internet.

Anybody have any ideas as to what's going on? I've checked all the cords and they're fine... internet worked perfectly last night, too.

Could you give us some more information about your setup.
Could it be a case of your connection not working and the wireless ones are going through another access point.
Have tyou tried rebooting your connection and trying again ?

If rebooting the connection means restarting the computer, I have done that.

I'm using Windows XP for one, Linux (Ubuntu) for another, and Windows 98 for a third computer. They're connected via a LinkSys router.

Nope I meant the router.
You need to ensure that the router is connected correctly.