Why is the Internet working everywhere except the main desktop?

I’m working on fixing it so that my mom can do her online classes and such. But it’s working on my brothers iPod Touch (which I’m on now), but it doesn’t work on the desktop.

The modem is fine, the wireless, Internet, and dsl are on… the Modem/Data cord is in the E4/Data slot… could that be it?

Also, when I press ‘repair’ under local area connections, it tells me that it can’t because of something about the TCP/IP. o___o

Any ideas? I’d rather not have to resort to calling my dad…. :/