missing operating system error

Common causes:

If you have a floppy drive, make sure there isn't a disk in it.

Your computer isn't seeing your hard drive. Check in your BIOS screen to make sure your computer sees your drive. If not, check/replace the cable and check the power connection to the drive.

If you have multiple drives, make sure that your BIOS is set to boot from the one with the OS installed.

If you are booting from a RAID - did you install the right drivers during setup?

Was it working before? If so, you could have a corrupt bootloader - you should be able to fix this with a repair, rather than a full re-installation. - Try booting from the windows DVD.

I booted to the windows dvd, no os found, it said to load drivers but the sources were all wrong. I just hit next and hit repair. It took 5 seconds and reboot and it was normal.  

Uh oh - well, I have the same problem, but trying to get VISTA to repair in said manner didn't work, it ground away for about 20 minutes and eventually came back saying it can't fix it, and seems to be pointing to a corrupt MBR, but I kinda figured that's exactly what the autorepair should fix?