An operating system wasn't found

Solution 1:

Go into your BIOS and change the startup order. Make sure your harddrive is the first drive it tries to boot from. This will make sure it won't try to boot from any USB drive or DVD, etc.

New BIOSses usually have a key to access the boot menu anyway which you can use to boot from different media in the case you need to install windows etc.

Solution 2:

I had the same problem and discovered that the mouse I had connected to through a USB port was causing the problem. I did follow the suggestion above to make sure the first thing to Boot would be from disc, but after that, it still gave me the same error message you received. I was about to give up when I tried unplugging my mouse and the computer then booted from the disc.