Sounds like the drive the computer normally boots windows from is not accessible and therefore the computer cannot continuing the bootup process by loading Windows for you. Since Windows (or any other OS) is not available, the only thing the computer can do is stop.
You might try removing any USB flash drives or CD/DVDs to make sure it is not trying to find Windows on them.
You might try removing any USB flash drives or CD/DVDs to make sure it is not trying to find Windows on them.