tcchen: Thank you very much for contacting the Intel® NUC communities. We are sorry to hear the NUC is not working properly.
Just to let you know, the tests done by Intel on the NUCs where done using Windows as operating system, so all the troubleshoot steps and suggestions we have available are in reference to that software. However there are users that were able to use Ubunto with the NUC successfully.
In this case, since you are using Ubunto, what we recommend is to visit their forums for peer to peer support assistance on this subject:
I also encourage all the peers viewing this forum, that if they have further feedback or recommendations on this matter, to post all the details on this thread.
Any further questions, please let me know.