change screen setting back to default settings

hi

try going to your computer or graphics cards manufacturers website and look for the drivers download section

look for your computer or graphics card model number depending what you have and download and install the latest vista graphics drivers

then try doing the screen resolution changes

http://windows.microsoft.com/en-us/windows-vista/Change-screen-resolution

Change screen resolution

Screen resolution refers to the clarity of the text and images on your screen. At higher resolutions, items appear sharper. They also appear smaller, so more items fit on the screen. At lower resolutions, fewer items fit on the screen, but they are larger and easier to see. At very low resolutions, however, images might have jagged edges.

For example, 640 × 480 is a lower screen resolution, and 1600 × 1200 is a higher one. CRT monitors generally display a resolution of 800 × 600 or 1024 × 768. LCD monitors can better support the higher resolutions. Whether you can increase your screen resolution depends on the size and capability of your monitor and the type of video card you have.

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or try this:

try a system restore to before this happened

http://www.windowsvistauserguide.com/system_restore.htm

if necessary do it in safe mode

Windows Vista

Using the F8 Method:

1. Restart your computer.
2. When the computer starts you will see your computer's hardware being listed. When you see this information start to gently tap theF8 key repeatedly until you are presented with theWindows Vista Advanced Boot Options.
3. Select the Safe Mode option using the arrow keys.
4. Then press the enter key on your keyboard to boot into Vista Safe Mode.
5. When Windows starts you will be at a typical logon screen. Logon to your computer and Vista will enter Safe mode.
6. Do whatever tasks you require, and when you are done, reboot to go back into normal mode.