A little background on my setup: I have Linux Mint 18 installed on one SSD and Windows 10 on another. I have the display plugged into the motherboard (a gigabyte board with intel graphics), but also have a nVidia gtx 1070, which I run headless on Mint to do computing work. After two weeks of running perfectly, I can no longer access either the bios or the Mint installation (and no recent Mint updates or software changes).
The following behaviors occur:
1) If I boot with the display connected to onboard graphics, I will arrive at the Windows login after a delay where there is no input detected and no BIOS splash screen. Once into windows, I can connect my display to either onboard or nVidia graphics and both work perfectly.
2) If I attempt to use windows restart options to boot from my Mint SSD or a linux live USB, the computer will boot directly to Windows with a delay as above.
3) If I boot with the display connected to the nVidia card, I get the BIOS flash screen briefly. Regardless of what key I press (I've tried them all and the keyboard is detected), it will proceed briefly to a black screen with a frozen cursor and then to an empty black screen. From there the computer will turn itself on and off three times. The cycle is as follows:
Turn On --> B_BIOS light on --> BIOS SPLASH SCREEN --> black screen with cursor --> black screen for ~5-10 s --> Restart --> M_BIOS light on --> immediate restart within 1 s --> B_Bios light on, black screen no BIOS splash --> Restart after 5-10s --> black screen indefinitely.
4) If I remove the nVidia card and connect the display to the board, the computer will continually cycle, turning itself off and on again, switching between M_BIOS and B_BIOS. In this configuration I cannot even boot into Windows.
Needless to say, I'm very frustrated and very stumped. I've tried resetting the Bios and CMOS onboard. Neither remedies the problem.