Various websites and a potential class action law suit talk about the problem of using the 8800 Series GPU with Vista. When running DreamScene, DirectX 10.0 demos, and video DVD's, a message pops up after a couple of seconds of a blank screen saying that Nvlddmkm.dll or Nvlddmkm.sys has lost connectivity and has been restored. In most cases the computer has to be rebooted to permanently stop the error once it has occurred even AFTER the offending program (such as DreamScene) has been stopped. In some cases, there is a BSOD pointing to Nvlddmkm.sys or some other error message, which requires a hard boot.http://social.technet.microsoft.com/Forums/en-US/itprovistahardware/thread/fd499e81-63d9-4ebf-8dcb-4eca24007afc/
Many solutions, including driver updates, elimination of older versions of the drivers, BIOS changes, and removal of Creative X-Fi drivers have been suggested in hundreds of blogs. None of them work in isolation for long. The most promising solution, the elimination of older Nvidia drivers lurking around in Vista has been acknowledged by Nvidia and they have introduced a new installation program/driver in their 158.15 release of April 12. This did not work to completely alleviate the problem.
Well, for me, I have fixed the problem; I simply installed 158.15 which slowed down the recurrence of the problem but definitely did not alleviate it, and then later, as part of my two month quest to solve this problem, as an experiment, turned off UAC. Everything has been running fine for 2 days including DreamScene, which is a record; DreamScene had not run for more than 5 minutes prior to this last step. I had never before been able to run the DirectX 10.0 demos that are downloadable from http://www.nzone.com/object/nzone_cascades_downloads.html which is now astounding me with its beauty and stability. I urge you to test this (less than perfect) solution or to get Nvidia to test it. I have “replied” to many of the blogs that I found about this subject and offered this solution; one person has responded telling me that it had fixed his problem too and one person had always had UAC turned off and AFTERWARDS installed the new drivers and nothing changed for him. It certainly would be beneficial, if this is "the" solution, to get the word to Microsoft and to Nvidia. Though I have gone on those websites to report my finding, I am not sure that it will be seen by enough people to give Microsoft and Nvidia an incentive to test. We al;so need some active participants to these blogs to carefully track down differences in setup that may affect this SERIOUS problem.
I have to say that I had this problem and this fix helped me out greatly when trying to fix my rig.