My Tivo Premiere will not boot up.... please help

I have two Tivo Premieres.

Unit G(good tivo) works fine. No problems ever.

Unit B(bad tivo) used to work fine, but now has problems.

I purchased unit B in October 2010. I turned it on and it worked fine for a few months. Then it started screwing up. It would boot up part way but not all the way. It would freeze up. I attempted the amateur repair tactics...... I cracked open the case, checked a few cables, unplugged the electric cord a few times, etc...... It finally started working correctly again(not sure why).

Now, a few months later, the bad Tivo will not boot on at all. I can hear the hard drive spinning and the green light comes on. But that is all. The yellow light does not flash. This Tivo does not even make it to the very first "Welcome" screen.

I figured that perhaps my hard drive might be the problem(e.g., maybe the image was bad). So I took the hard drive out of the bad Tivo and I connected it to the motherboard of the good Tivo. It booted up fine. So I concluded that the hard drive is not the problem.

Also, I thought that a bad power supply might be the issue. So to test that, I took the power supply out of the bad Tivo and put it into the good tivo. It booted up fine. Also, as a further test, I took the power supply out of the good Tivo and put it into the bad Tivo. That did not help anything. So after both of those tests I concluded that the power supply must not be the problem.

At this point....... I am not sure what to do. I have a lot of experience working on the old series 2 Tivos. But I do not have much experience at all with the new Tivo Premieres.

Suggestions?

Thanks,

TC