Hi Paul - Thank you for your response. Good news! Samsung hinted that my specific monitor model had reported compatibility problems w/ W7. So to test that theory, I bought a new monitor today and, so far, all is well. Doesn't solve my need to understand root cause but it solves my need to be fully productive again. :-) What I do with two beautiful 21.5" Samsung monitors remains to be seen.

I don't understand your comment about 64-bit. I've been on Windows 7 64-bit from the beginning and, until three weeks ago, had no problems. Could you please elaborate? We didn't try reinstalling Windows 7.