Macbook won't load pages over wifi

I hope someone can help me.

I have a Macbook that connects to my WiFi network but does not connect to the Internet. Other devices (iPad, Android phone, Roku 3) get to the Internet just fine.

I am not running any anti virus or firewalls except what came with the mac. I am on OSX 10.9.1 and have tried connecting to the internet via Chrome and Safari as well as running Traceroute and Ping in the Terminal screen. When I use an ethernet cord plugged directly into my DSL modem (which is also my wireless router), AND turn off the wifi, the macbook connects to the internet just fine. If I am plugged in to modem but leave Wifi on, Ping and Traceroute (and browsers) fail to connect.

I have tried restarting the modem/router and restarting the macbook. I tried clearing out all the remembered networks under Settings->Network->Wifi->Advanced->Preferred Networks, turning off Wifi, turning it back on and then re-connecting to my wifi network.

EDIT: I tried connecting via Wifi using my phone as a hotspot. Although I could connect to the network that it created, I could not connect to the Internet. In other words, something is screwy in the macbook's Wifi connection, right? I think that is the problem since I can not connect via wifi on two different networks which DO work with other devices AND I can connect to the Internet on the Macbook by plugging in the Ethernet cord.

When I called my ISP (CenturyLink), the technician checked my modem and said it was fine. He also said he could see my macbook on the network (he identified it by name so I know he wasn't making it up).

This is a new problem that started today. I have not made any changes to the network, modem, router or macbook.

Thank you for your help.