Try starting it by keeping the power button pressed until it beeps. Probably about five seconds.
I hear beeping you mentioned, still a DEAD BRICK
I am sorry you are having problems with the NUC.
I see you have performed many steps. The link that Stu.in.the.UK has provided is very useful.
I would recommend trying that and in case it is still failing, You may contact our local support for them to get some information and replace the unit if necessary.
Here is the contact: