I'm having the smae type of issues. I have an ASUS P8H67-V (REV 3.0) LGA 1155 Intel H67 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard with UEFI BIOS.
I've checked for viruses, exclamation marks in device manager, etc. and nothing.
The only things I can think of are loose connection or dying motherboard. Am I missing anything?