Hello,
For one, could you try performing device recovery, by uploading the firmware via bootloader menu? For instructions, please refer here.
Of that does not help, If I understand correctly, the device responds, if you connect to it via ethernet cable and connecting interface has a static IP set?
Have you tried WebUI/SSH access? Have you tried cable connection with different devices? Do they connect correctly?
I would also want to check if the device logs generate any related entries. Connect the router via ethernet cable to your computer. Connect to it over WiFi as well, to have access to the device. Login to router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. Attach the downloaded file by editing your question.
The logs in the file might provide more insight into the issue.
Best regards,