|Thank you so much for responding. You can't imagine how relieved I feel.|
I've removed everything and inspected the motherboard. I don't see any shorts. I did use 9 standoffs to hold the motherboard because there were 9 holes for screws. However, there were only four screws with motherboard, so I only used four screws. I am removing all standoffs except the four where I will actually use screws, as per your instructions.
I did not apply the thermal paste as described on the Arctic Silver site (I spread it out with a credit card), so I am in the process of removing the huge Mugen 2 cooler that I attached. That cooler required that I remove the cooler backplate from the back of my motherboard and replace it with a larger one supplied by Scythe. For testing purposes, I am going to install the smaller cooler that came with my i7 processor using the technique on the Arctic Silver site. That way, if the problem is due to the large Mugen backplate, this will eliminate that.
I do have one more bit of information for you. There are two connectors from the power supply to the motherboard: 24pin and 8pin. When I removed the 8 pin connector and only had the 24 pin connected and pressed the power on button, the motherboard did seem to power up (i.e. fans continued, led lights on motherboard continued) past the 1 second limit. I shut off the power after 2 seconds because I didn't know whether not having the 8-pin connector connected was bad. I also wanted to point out that although the Corsair 8-pin connector fits into the Gigabyte 8 pin sockets, the pattern of round and square pegs/holes are not the same. The socket has 4 square holes and the connector has only 2 square pegs. I don't know if this is significant or not. Do I need the 8-pin connector connected? Is the hole pattern mismatch important?
I'll report back when I have the cooler replaced and put together the minimum system as you suggest.
However, I really want to ask you what you mean by bench-testing the components. I didn't see any reference to this in the sites I looked at (PCMech, PCWorld video, Tom's hardware sites). Can't I go back and bench test them now? Or what should I have done for the next time?