I just set up my network and it works perfectly for the LAN but I have no internet...I connected it perfectly I'm pretty sure. I connected one cat 5 from computer 1 to slot 1 in the router, then I connected computer 2 to slot 2 in the router, then I connected one cat 5 from the modem to the WAN slot and plugged in the router power but I don't have any internet, the LAN works flawlessly but my internet just isn't working.
P.S. it's not that the internet is down, I tried it just before I hooked up both computers to the router and it worked.
FWIW - try unplugging the modem (power from the wall), don't just push the button on it, but power it off for about 1 minutes, then plug it back in.
Beyond that, you will need to go into the Router config and make sure everything is set to the way it should be, and only you know what that is, we don't know your ISP or the addresses they use.
You also didn't say what kind of Router you have, or exactly how your network is configured. This also may be better answered on other websites like www.helponthe.net (Tech Support Guy), where a lot more people surf than here.