To check TCP/IP go:
Start, Control Panel, Network Connections --
if no Connections are listed click on the Network Wizard.
If Connections are listed click on one and when a window appears stating This Connection uses the following....scroll down that list and look for TCP/IP
If TCP/IP is missing press Install and follow the instructions.
If TCP/IP is present highlight it and check Properties and make sure Obtain DNS and IP Address automatically are both ticked.
From some of your comments, I think you probably need some hands-on help here -- larger computer retailers have services like Geek Squad and some small computer techs advertise in local newspapers. Might be worth paying someone to sort out your machine.
However, with a 2004 vintage machine I think the cost of maintenance might look unattractive compared with that of replacement.