This means that your hard drive is no longer recognised, or that some key boot files are missing.
It's probable that any one of the following files got deleted:
autochk.exe, boot.ini, bootfont.bin, NTDETECT.COM, ntldr, bootmgr, cmldr.
The followings are not realy needed, but legacy demands that they be present (they are empty files):
AUTOEXEC.BAT CONFIG.SYS MSDOS.SYS IO.SYS
Get a Linux live CD and use it to boot.
Check that your main hard drive can be accessed and that the preceding files are present.
IF your boot drive can't be accessed, it may be that it's dead.
IF there are missing files, it's probable that you'll need to reinstall Windows.
Electro, July 2011
