Hi MigLancer,
If the problem occurs on another monitor, the problem may lie with the video card or the monitor cable. Are you able to try different ones?
Also, are you using the latest drivers available for the video card? What video card are you using anyway? Also, what operating system are you using?
Here's another thing you can try: restart your PC and when you see "Verifying DMI pool..." start clicking on the F8 key or hold the Ctrl key to get to the Boot Menu. Choose Safe Mode and let the PC boot up. Once in Safe Mode, go to Start> Settings> Control Panel> System> click on the Device Manager tab. Once in Device Manager, click on the "+" sign next to the monitor icon and see if you have multiple monitor entries. If you do have multiples, delete the extra entries (or delete them all...Windows will re-detect the devices) and then reboot the PC. I don't know if this will help with your problem, but it's good housekeeping to keep your system "clean".
Cricket