Disabling “Rotate About Scene Floor”
When enabled, “Rotate About Scene Floor” will give the impression that your workspace contains a floor. This means that rotation around the X or Z axis will stop as if running into an invisible wall. To disable this setting, select “View” from the pull down menu on the top of your screen. Under “View” select “Modify” and then deselect “Rotate About Scene Floor”. The image below shows where this setting is located.