Do you have more than one monitor on your system, or did you at one point and time?
If so, go into the launcher (Blizzard launcher, not OW) go to Game Settings by clicking on the sprocket next to play, then selecting it, and select “Reset In-Game Options”. This should default everything back to when the game is clean installed the first time, including any monitor or video card settings.
If you’ve never done that, it will still maintain your previous settings in the game when you reinstall the game. You have to tell it to reset to defaults to get an out of box style configuration.
Any system specs would be helpful, configurations, etc that might help troubleshoot the issue.
Also, if you have a laptop, and you’re using an external monitor with it, it’s entirely possible the game could be displaying on your laptop screen rather than your external screen.