My parents' computer stopped booting from the HDD into Windows: it's showing a "Missing operating system" error. I tried burning a Live CD of the latest Ubuntu and booting from that, but it's giving me the same error. I know the Live CD works (I can boot my laptop from it). It does seem to be actually trying to boot from the CD (when I boot with the CD in it takes longer to get to the error message than if I boot with the CD out, or if I change the BIOS boot order to skip the CD drive; and the CD drive light is active during that time). Might this be a hardware problem? Are there common problems I can look for that might cause this?
I've had that happen to me when I tried to use a live DVD on a system that can only read from cd's.
Make sure that your live CD is not in fact a live DVD. You can also try blowing the dust out of the cd-reader. There are also special cd's with brushes on them that clean the lense in cd/dvd drives.
Try getting the newest version of the live cd. New versions add support for new hardware.
You can try replacing the data cables on the drives. If these drives are IDE, you can play around with the jumper settings. Sometimes cable select causes problems. You can try manually setting the drives as master or slave (if they share the cable with another drive).
If all this fails (in addition to previous suggestions). You may have a broken cd/dvd drive in addition to a broken hard drive.
There's a whole list of reasons why that could be happening.
It might be that your BIOS isn't detecting the hard drive, the Master Boot Record (MBR) could be malformed, the hard drive itself could be damaged, missing or corrupted boot files caused by a virus.
First thing to do is to check whether or not a USB drive is plugged in, sometimes your PC will try to boot from it and display Missing Operating System. If something is plugged just unplug it and restart.
If that didn't help your second option would be to check the BIOS setting and make sure your drive is in fact recognized. If it is recognized try accessing the recovery console (not sure what version of windows you're using) by booting with the windows cd, click on Repair your computer, select Command Prompt and type
Once that's done you could fix your MBR by typing
If you can't boot neither from hard disk and nor from CD, you have there a very serious hardware problem.
Whatever advice we could give here might cause the total lose of the hard disk.
This is much better handled by a repairman, that could salvage the computer by replacing the failing component, rather than by you yourself following our own wild guesses.