Hard drive stops POST

I am upgrading a pc. Installed new motherboard, cpu, and memory. I first booted with a floppy start-up disk, worked fine. Then I installed the hard drive, re-booted from floppy, and formatted the HD. All went well during format. When I restarted again, it would not POST, not even beep. It will boot if I unplug the HD, booting from floppy. I tried another HD, same results. Any ideas?
Thanks,
Doug