No boot after new HD on first built PC

i7, Intel DX58SO, 3x2GB Corsair 1333, Sapphire Radeon 4850, Antec 900, Corsair 650 W, Seagate Barr 640GB

This is my first PC build, 2 weeks ago. All was well. Then last night I added a 300GB Velociraptor, Ran ok WD diagnostics on it, then used WD DataLifeguard tools to do a copy including boot stuff to the new drive. All looked well for 30 min. When I came back 2 hours later the system was dead.

The situation now:
-MOBO power light on and fan lights (case and mobo)
-no beeps
-no mobo lights except green power light
-nothing on the monitor ( GPU fan is not on)
-at power on, it starts up for 6 sec. then automatically restarts, then remains powered on but dead except for fans and lights.

I've done this with no change in symptoms:
-removed all drives, HD and DVD
-moved RAM sticks around and tried one at a time
-moved GPU to different slot and different power cable
-CMOS- removed battery for one hour per Intel instructions
-checked and rechecked all cables and connectors
- removed GPU
What the heck can I do to pursue this?
Also, I've unsuccessfuly searched for a document which shows step by step details of what happens with the mobo/CPU after I press the start button. Any links here?

Thanks a lot. Jim