Can't connect to internet (problem with computer)

The new computer I just built can't connect to the internet and I've narrowed it down to a problem with the hardware. Any ideas on what I might have missed when building the computer?

Are you sure it's got to do with your hardware? Try calling up the company of whom your with.

I also had the problem when I hooked up my new system to a LAN cable. Turns out I didn't install the druver :P I felt like an idiot then