Maximum ram speed for that Gateway would be DDR3 1333. The G.Skill is rated at DDR3 1600. Depending on how good the board is, some will just automatically down clock the ram to DDR3 1333 while others will not boot up at all.
Best thing to do before upgrading is to update the motherboard bios so it will support newer ram.
G.Skill also have ram rated at DDR3 1333