The window is resizeable. If you are having issues resizing the window, try right clicking on the title bar and then selecting resize.
All erased saves are backed up and can be restored with a simple process.
If some files are missing or corrupt you can try verifying the install through Steam. Right click on the game icon within Steam and select Properties. In the newly opened window, select Local Files and finally Verify Integrity of Game Files. Steam will then fix the game.
Click the support bubble on this page to submit a support ticket!