No boot device found?

I have a lot of about 10 optiplex gx520's all having the same problem. when powered on the machine stops after the dell logo and gives an error
"no boot device found - primary disk failure" or something of the sort....well if i press f12 and select the sata drive from the list of boot devices it boots straight into windows...restart the pc and bamM! "no boot device found - primary disk failure"

I have tried telling the bios what priority to boot and it still gives that error when i turn it on or reboot the machine. I can get into windows by pressing f12 and selecting the sata drive to boot everytime.

Is this a cmos battery problem or is there something else going on here. My original determination was that all 10 machines had HD failures now, Im wondering if its just the CMOS batteries?

Anyone else have any input on this? I apologize if I have been vague at all if I have left something out please just lmk.

-James-