Thanks, Rolli59! I'll give it a try. I'll try anything at this point. Shouldn't the audio beeped a few times to let me know the system was hungry for delicious keyboard though?
BTW, I tried a 600 watt power supply (Cooler Master) that did the same thing, i.e., turning off after about 5-10 sec. That ps only has a 4 pin CPU power supply plug instead of the 2 4-pin plugs in the ps that I listed in the original post, and I wondered if that was the reason for the shutoff: either too little power on the first ps vs not enough pins in the plug on the second.
Also, did I mention that this is my second Gigabyte board? I've been getting a lot of eye rolling when I say that I got a Gigabyte board instead of Asus, or even ARock.