Couple things to try
Clear the CMOS with the button on the mainboard.
Switch BIOS's to the backup BIOS.
Test bare board, only have only your display plugged in, remove all hard drives, SSD's, USB devices, DVD's, etc. Then see if your boot time is any faster.
http://download.gigabyte.us/FileList/Manual/mb_manual_ga-z170x-gaming-g1_e.pdf