Can you boot into safe mode? If so boot into safe mode with networking, download the latest forceware from Nvidia.com and install it. That should fix that problem.
As for the monitor, if having the new card doesn't fix it, I would contact Acer themselves. I own the very same one, and other than a few minor annoyances involving the backlight, it rocks. A refresh rate of 60 is all that monitor supports. As to your PC running slower than beofre this monitor, that may be because you're running at a higher resolution?