there are patches on the screen. what could be the reason and how to correct it

Are they nice Patches?

Can you get a screenshot?

Is this a new problem? Any new hardware or software?

If a new problem try System Restore:

System Restore
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You might try a System Restore to a point prior to your problem:

start > All Programs > Accessories > System Tools > System Restore


If that doesn't help I would uninstall then reinstall my graphics drivers.

If you use our scan at the top of the page we could ID your graphics card.


You could also verify the graphics issue by booting into Safe Mode and see if the issue persists:

Safe Mode
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Can you get into Safe Mode?