I have machine with an Asus P8H77 motherboard, which contains a series of SATA disks. One of them has grub2 installed, and boots Debian.
I have the boot disk defined as the priority in the bios, and disabled other boot options.
If I start the machine, it goes through the bios, right up until the point that the grub2 menu would display, then it reboots.
If I hit the key that allows me to select the boot drive at boot up, and choose the right drive, it reboots.
IF I hit the key that goes into the bios screen (Easy Bios), there is another option for choosing the boot device. If I use this to choose the right boot disk, it boots up fine. Note this isn't a configuration option, it is just another boot menu.
So in each of the three cases, the same boot disk is being chosen, but will only boot from it if I go to the bios first.
It is almost like there is a race condition, and the boot disk is not ready, and going into the bios gives it enough time to settle.
What could be causing this?