I have the same device and mine works fine with the inbuilt nic, make sure you are selecting amd selection in the boot menu press space bar when the print appears and reselect amd again that worked for me on update 9
what packages do you have installed on it as surveillance station keeps it awake as do some other programs, i had the same problem so i removed alot of them that i dont really use and now the nas goes to sleep when not accessed for a while
ignor above after putting the monitor and keyboard back onto the nas and re selecting the boot option in juns it decided to work now working on update 9
been there done that still gives me "the the system has failed to perform the requested operation, there is an unkown error" as soon as i click onto the "log in to or register a synology account" bit on the quick connect page within the DSM