I've seen this and it happened to me when I had the drive on the second IDE channel or as a slave when it should have been the master. Correcting my mistake cleared it up.
I have a Dell optiplex 260 that I changed the hard drive in now in going from post to boot it says "primary hard disk not found press F-1 to continue F-2 to setup". The setup shows the hard drive correct I had no trouble loading Win XP Pro going to the Dell support site down loading the drivers and updates. After I press F-1 windows boots fine and the computer works perfect. "My computer" also shows the hard disk drive as "C".
Any help would be appreciated.