How can I fix this issue with connecting to the Internet on my Windows XP computer?

[Spec2jeti]

My brother got an old computer from our grandpa. We set it up and it works perfectly except for one thing. It will not, under any circumstance, connect to my WiFi. I have tried everything. It won't even come up with my internet. I plugged the Ethernet cable into it. The computer didn't even bring that up. The computer asks for a username and password. Then, it'll have to call my ISP. I even tried replacing the network adapter. That didn't work. What can I do to fix this? I know it has Windows XP Home Edition. It has 2gb of RAM. And a 2.99GHz dual-core Intel Pentium. The computer is quite a few years old. The specs I'm not for sure about. I believe those are the correct specs.
The network adapter might be around 6 years old. My internet is only 3 years old. I'm not quite sure what other info you might need. Every other device in the house works. It's just that computer.

 

[jsmithepa]

The computer asks for a username and password. Then, it'll have to call my ISP.

I don't know what this means, be more specific. Why do you have to call ISP? No other devices in the home work? Is this is a new ISP service?

Be methodical, tell us what logical steps have you taken to troubleshoot other than "it doesn't work."

 

[FALC0N]

If it's asking for a user name and password over Ethernet, it sounds to me like its configured for PPPoE. The wifi issue is likely caused by an older wi-fi card not supporting newer protocols, but we will need a lot more Info on your hardware setup before we know for sure.