Let us get the model number correct first so we know what we are dealing with. You mean NUC5i5MYHE, correct?
Power on holding the power button down for 3 seconds. This should result in display of Power Button Menu. Use F2 to get to BIOS Setup (Visual BIOS) and clean up config. Can also try clearing CMOS, first from menu and then by unplugging CR2032 battery if necessary.
Hope this helps,