If that doesn't work, try resetting the Workspaces: Reset a workspace Reset the current workspace to return to its original, saved layout of panels. 1. Do one of the following: • Click the Workspace menu icon and select Reset to Saved Layout. • Choose Window > Workspace > Reset to Saved Layout. from here: https://helpx.adobe.com/premiere-pro/using/workspaces.html
If that doesn't work, try creating a new project and import the old one into it.