First boot trouble

[cath_jockey]

I have successfully built a few PCs in the past and am working on 6 identical machines currently. I have assembled two of these with the components listed below. Both have identical issues. When the first boot is attempted, the CPU fan spins and the case lamps light for about one second, then both go off. In about 5 seconds, the system powers on both again for one second, and the cycle continues until I shut off the PS.
I have disconnected every cable but the PS and the power switch, used one stick of memory in each slot, reconnected all cables, removed the video card, all with the same result. Any thoughts? I built the second machine with the notion that if I had a faulty component, surely two wouldn't be bad.

CASE APEX|PC-389-C RT
MB ASROCK H55DE3 LGA1156 R
VGA SAPPHIRE 100292DDR3L HD5450 1G
PSU LOGISYSCOM|PS480D 480W RT
CPU INTEL|CORE I3 540 3.06G 4M R
MEM 2Gx2|GSK F3-12800CL9D-4GBNQ R
HD 500G|WD SATA2 32M WD5000AADS
MNTR HANNSG|LCD 19" 5MS HW-191APB R
DVD BURNER LITE-ON | IHAS124-04

Thank you in advance for your help.

[cath_jockey]

I figured out my trouble and it is working fine. Dummy me didn't plug in the CPU PS.

[Rob]

Way to keep after it. Nice job.