Monitor vs video setting or both
Depending your monitor, enter the monitor's physical setting OSD(on-screen diags), just enter it. Review the manual if need be. Once it pops-up its OSD, find the "auto-setting" button and hit it. It will auto-adjust to the best defaults of that monitor. Once done, leave it alone. (dealing with the monitor itself)
Now, compare the display on your PC, if it corrected, leave it alone. Otherwise, using my previous post instruction find a resolution that makes it alright. This allows the video port/card to become the best match to your monitor. You may need to play with it as there are various resolutions and setting. It should give an example of how it's applied or just does it, select or refuse. Try another if need be.
The actual last resort, would be using a "restore point" to a date prior to mishap. use that date and allow to return when everything was OK. However, this also returns to that time period as it was. This could undo any changes, or updates, etc., but you correct your problem. It won't effect data though. Google for restore point feature for Win7 usage.
Make sure you're not dealing with "font size or content display" variation. Since, you mention left and right sides vary, I assume its a resolution/setting issue.