I installed a power supply and removed the floppy disk from a Dell Optiplex GX520. Now when I turn it on, it says there is no serial ATA SATA-2 nor parallel ATA, Path=0 (Pri Master.) Everything is working so I don't know what the problem is.
Have you checked the boot sequence in the BIOS? If not, enter the BIOS and make sure the removed floppy drive is not selected as the first boot device.