As far as I know, the Vsync signal is sent to a register of the cpu by the graphics card. It's them up to the program to make use of it. Contrary to EG the Atari ST which allowed a Vsync-triggered Hardware-Interrupt, PCs must poll the register. (Correct me if I'm wrong)
To me this DVI cable problem sounds like a driver bug. Don't know much about DVI, but I guess it's a digital transfer of data from PC to Monitor. If so, a certain transfer speed is required. Maybe it's not fast enough. Or maybe there's bad snyching of multiplexed data on that cable, in both directions.
Did you update the driver and/or search some NVidia forums for this topic?
To me this DVI cable problem sounds like a driver bug. Don't know much about DVI, but I guess it's a digital transfer of data from PC to Monitor. If so, a certain transfer speed is required. Maybe it's not fast enough. Or maybe there's bad snyching of multiplexed data on that cable, in both directions.
Did you update the driver and/or search some NVidia forums for this topic?