Can only look while aiming down sights

Today I was playing Borderlands TPS when i noticed i had to something important. I pressed escape to put the game on hold and because i was on fullscreen i f4 out (to be able to see the dock) and pressed “hide” to remove the paused game background. When i finished the mouse would work except when i aim down sights. i have tried quiting, re-launching, etc… Does it have anything to do with the “hide” or “f4” and CAN IT BE FIXED!?