Sounds like the EVGA or NVIDIA driver is not working with Windows 8. Did you try getting a Windows 8 driver from NVIDIA, rather than EVGA?
You seem to be Ok using the onboard graphics, despite using the Ivy Bridge CPU compatible UEFI version with your Sandy Bridge CPU. Have you done all the driver updates required by UEFI 2.10? Yes I know you have 2.30, but what did you have before 2.30?
If you have a PCIe 3.0 setting in your UEFI, you can't use it, your CPU does not provide PCIe 3.0, only Ivy Bridge CPUs do.