I am running 12.04 64-bit and am dual booting with Win7, for full disclosure, although I suspect that has nothing to do with my problem.
The boot-loader(GRUB) fails to load often and I will be presented with a black screen with a single blinking line. This has happened to me eight out of ten power cycles now and I can fix it consistently, however, I have no idea why it happens.
My current fix is to boot a live CD (I've tried both KNOPPIX and Ubuntu with the same result) and that's it. Somehow booting with the live CD is enough to "wake-up" my hard drive. I then reboot and GRUB magically appears again.
So what is going on? Is it possible that a program is corrupting my MBR and the live CD is restoring it? How can I narrow down the possibilities? Thanks.
Additional
This is still a problem. I'm convinced now that it is not hardware related as I've spent the last month and several boot cycles on Windows without a hiccup. Recently when I started using Ubuntu again the problem started again.
I am more interested in figuring out what is going on rather than actually fixing the problem. Are there any tools, logs, etc. I can use to unravel this mystery?
Update
I can now consistently recreate the issue. It seems that if the computer is put into suspend mode at any point prior to restarting, the problem comes up. The computer goes into and out of suspend mode just fine but when I restart the system it fails to boot. I've tried this command before and after suspending the computer:
sudo hdparm -I /dev/sda > hdsettings.txt
Then I ran a diff on the two files and found that one thing changed: under security settings frozen changed to not frozen. I have no idea what that means but it's a difference anyhow.
Best Answer
EDIT: It seems like there is no error with Grub so this answer is not applicable. Sorry. @Web-E seems to be on the right track.
Boot from the live CD. Open the terminal
Press Enter - Then type:
Then open boot repair. Perform recommended repairs. If that does not fix it then paste the link here for the boot summary.