My desktop PC was hooked up to my TV and would randomly switch to using the TV as the main monitor often disabling my monitor. I thought it was my NVIDIA card so I upgraded to a newer ATI card. The new card has 2 monitor outputs and a S-video output. The problem no appears to only happen overnight. The next morning my PC is still on and awake but the display is changed to a lower setting. I have to enable a second monitor, which i do not have, before it will allow me to fix the resolution of the monitor I do have. Right now I have a bigger problem where it looks like it switched the TV to being the main monitor and I no longer have a TV hooked up (Its mounted on another floor of my house) so I cannot get to the screen to fix the problem. I tried plugging the monitor into the other port (sometimes it just switches ports) but that is not the problem. Thanks for any help.
ATI Radeon HD 4650 ver. 8.620.0.0 I don't remember what the driver name and version for the NVIDIA card was but had the same problem. Pretty sure its a Vista problem and not a card problem. (2 cards same problem).