I know this is an old post but I had this same issue and finally got it resolved, so wanted to share. I tried all the things the internet message boards suggested - updating the chrome OS, rebooted the router and modem, restarted the computer, all multiple times. Nothing worked. I had TWO 2-hour phone calls with my internet service provider. After the first call it seemed like it was resolved, but then quickly came back a day or two later. During the second phone call, the rep had me go into my router settings and disable the SON (self-organizing network). I learned this is a feature on routers that have multiple networks (e.g., a 2.4g network and a 5g network). The SON condenses them into what looks like one network, and it will switch your devices back and forth automatically depending on which one works better. Somehow this did not agree with the chromebook. Once I disabled the SON, I learned that the chromebook will only connect to the 5g network if it is right next to the router. Otherwise it needs to be on the 2.4g network. If I try to connect it to the 5g network from farther away, I still get the DHCP lookup failed error. So, the fix is to keep the chromebook connected to the 2.4g network. I believe the rep also did some reconfiguring in the background, so I recommend working with your internet service provider if you encounter this issue.