Hello mate
Please list all the USB and SATA port devices you have fitted to your motherboard.
Here is what I would do.
I am assuming you do not have an OC.
Go into bios and save your profile.
Exit bios.
Remove all devices from your SATA ports and USB ports - leave the OS drive and your mouse and keyboard only.
Now back in bios F5 to reset defaults.
F10 and enter to save and boot to OS.
Your system should now fix the OS drive as your first boot drive. I am assuming that your OS drive is in the Intel 6G port?
To help us help you - please provide as much information about your system and the problem as possible.