This is what I found out. You were correct when you said a PCI-E slot rarely goes bad. I installed a new MB (ASRock 4785GM-LE) and had the same problem. Man, this was getting frustrating. The solution to the problem was I had to install a fresh copy of Windows 7. When I first put the MB in, I thought I got lucky not having to reinstall all my applications. But after the problem did not go away, the last resort was to install a clean copy of the OS and take it from there. If that didn't work, then I was at a loss. Lo and behold, the fresh copy of Windows 7 and the video card installation did the trick. Everything works as I wanted it, and I'm glad it's over. I'm sure my old MB and PCI-E slot are fine, but I really don't care. It works, and if it ain't broke, don't fix it. I can only assume something in the OS didn't like something, and a clean install took care of it. Consider it a learning lesson, I guess.
Again, thank you for your time in troubleshooting this issue.