If you are using Windows XP, then your OS should not care if a monitor is hooked up. If using Vista, your OS may not be happy with you for unplugging the monitor.
The video driver update message for your 8800 most likely had nothing to do with folding. Which driver version were you using before the update? Which one now?
I have a GTX260/192 SP and it has been folding steady for months. I am using the most recent NVidia GPU driver, I think it is version 182.06.