Someone may not be very familiar with BIOS, and we will show you how to enable XMP with Gigayte Z77 motherboard here

Before enable XMP, please update with latest version of Motherboard BIOS and clear the CMOS.

OR, you can manually adjust the BIOS as the memory Specification:

Select the DRAM frequency & adjust the Selectable to expert:

Adjust the Timing

Adjust the DRAM voltage

After you adjust/enable XMP profile, make sure that you save the changes & exit.

Also, you can check the DRAM frequency/Timing by CPU-Z