A day or three ago, we lost power here. I was able to halt the system before the battery backup ran out, but when the electric company restored power, booting up threw me into a grub rescue> prompt along with ‘file not found’ or ‘no such file’ I forget which. No other machine available to get on the ‘net for instructions, and what I thought were bootable usb sticks would not boot (even after poking around in the bios settings for this Asus M4A89GTD-PRO/USB3 motherboard). No cd|dvd drive in the machine. I’m an ignoramus about what grub rescue> means and about how to boot from that prompt.
So, pulled off the case’s side panel to check the power and data cabling for the boot drive (and the other two drives while I was at it). Too much work to get access to the cables, so took a close look at the switches on the motherboard, maybe something’s in the ‘wrong’ position? This board has an AMD Phenom II X2 B55 Processor, but I’ve unlocked the cpu so it’s an X4. I noticed that the led’s next to the core unlocker switch and the turbo switch were not lit. Unplugged the power cable to the machine, flipped both those switches to the other position, reconnected the power cable and the system booted without a problem. No more grub rescue>.
Moral, print out grub rescue> how to’s, print out that motherboard pdf manual and have tested bootable media on hand.