Having issues connecting with new modem

I recently upgraded my connection speed, and now I'm having issues connecting to the internet on one of my computers. CenturyLink sent me a new wireless modem that my desktop PC does not seem to like. It's an Actiontec Q1000. My mobile phone, tablet, netbook, laptop, girlfriend's laptop, and iMac all have no issues connecting. My desktop PC does. Both the iMac and my desktop are connected via ethernet, and the iMac connects fine. This is making me think it's my PC acting up. When I run Windows troubleshooting I get the following errors:

- Local Area Connection doesn't have valid IP configuration
- The default gateway is not available

My girlfriend's brother set up the modem when it came as I was out of town. I'm not sure if he may have done something or what. Any idea on how to fix this?

And yes, I have tried restarting the modem and my PC several times. I got it to connect once, but after waking it from sleep sometime later it would not connect again.

Do you have the password for the modem? Log in and check the DHCP settings -- make sure it has enough local addresses. It sounds like you have a lot of local computers, and if the DHCP server is set with a small address pool, it may be running out before your main PC gets one.

That was it. Thank you sir.

Boy, I wish all my guesses were that good!