I suspect that, as usual, I did not give enough information. These are files recorded with Growler Gun Cam, which will capture any video on the display, no matter what the source program. It even will capture youtube videos and the like. GC converts them to .avi files. I have been using the divx codec for this for some time.

The .avi files that no longer work include those that previously worked (recorded before the new video card). Unless something has happened to the divx codec (I can't imagine what) I can see no reason why the old files don't work. For that matter, I don't really understand how a video card can affect this as it only supervises what appears on the screen, not how things are recorded, right? But, if I knew all about this stuff, I wouldn't be asking here, would I? Even so, I know that, because this happened after the nVidia installation, there must be some connection, no matter how strange.

Thanks for the info, I'll look into those things first.