well, I reset the BIOS to optimized default, and the card works again...(like magic)
So, apparently, I think I messed up some BIOS settings when I was messin' with it.
thanks everyone!!
OK, I have 6600GT and I have used it for a while and it has been great. Recently, I took the card out for like 2 weeks due to it's noise (and I had exams for the past 2 weeks). In another word, I was running on onboard graphics...
Now, I plug the 6600GT back into the PCI-Express and turn on...