Hi,
1. Did you make any changes to the computer off late?
2. Have you updated the display drivers?
3. Do you have any games installed on the computer?
I would first suggest you to check the computer manufacturer`s website for the latest drivers available and update the same.
Games often change the screen resolution and so do some other programs. You can try performing a clean boot process to find out if there is any program or application causing this issue. Follow this Knowledge Base Article.
http://support.microsoft.com/kb/929135
Note: Make sure you put the computer back to Normal Startup once troubleshooting is completed.
Regards,
Syed N – Microsoft Support
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