System Admin and PC Support background with 25 years of experience here. Same problem with a Gigabyte z68a-dh3-b3 and I5-2500. Worked great with Windows 7. After installing Windows 8 and the same issue reported by others in this post. Tried all of the suggestions with no luck.
Gigabyte support was a waste of time. Several monitors that I cannot use under the current setup. A drain on
production.
Hesitant to purchase another Intel based board. Looks like AMD and another brand of board may be the solution as Intel and Gigabyte are apparently not offering a solution.