If you have your Windows CD, Id put it in and reboot. When the CD loads, I'd try a repair or a recovery. If that doesn't work, I'd try a reinstall of Windows that keeps the old files.
Take the floppy disk out of your computer and turn it on. If that doesn't work, unplug all of your USB storage accessories (external HD's, etc.) and turn it on.
check your harddrive. If that checks out. then maybe your bootsector is gone/messed up. Might have to reinstall.
Hmm, I might try and boot from a Linux thumb drive or live disk and see if I could access the windows files and see if the files could be replaced.
Pretty much this. When no OS is found, it means no OS is bootable, which means a basic file issue. Time to reinstall Windows. Or buy a Mac.
Typically when I encounter this, Windows is trying to boot from something plugged in...i.e. a floppy Disc, or occasionally an external HD. Money says he ejected or unplugged it, and it worked.