The 7770 and 7750 use PCIe 3.0 signalling but PCIe is backward compatible all the way to PCIe 1.0. Your motherboard is most likely using PCIe 1.0. Occasionally, you may need a motherboard BIOS update to get it to work but most of the time that's not required.
Thanks! I am not sure if my PCIe is 1.0. I gave my motherboards link. http://www.gigabyte.com/products/product-page.aspx?pid=3505#sp
In the specs it only says (1 x PCI Express x16 slot, running at x16) it doesn't say PCIe 1.0 or 2.0.
And Just to be Crystal Clear> PCIe 3.0 Cards are Compatible with PCIe 2.0 & 1.0 Slots?