Iīll bet a fortune on that it is your memory. Double check voltages and timings. Try losening them and up voltage (donīt kill'em!). Being a core i7 your max mem voltage is 1.65V I think (also double check mem compatability with your MB, Gigabyte list them on their home page. Not exclusive list but might be helpful). You can also try swapping the DRAM into the two free slots and see if that works. But again, timings and voltage. Check mem makers homepage for settings!
Someone suggested Windows 7 / Gigabyte MB issues. There are no such issues. Run a Gigabyte MB on one of my Win 7 machines (P45 and E6600 though), no issues, but it is very picky with ram. I canīt populate all four mem slots, it will just freak out. And voltage / timing same thing, and I run high-end Corsair sticks that are compatable with MB...