Wow… never seen that before.
You can give a try to use the “reset perspective” button of the toolbar, and possibly restart your DS.
If it doesn’t help, my guess is that your workspace is somehow corrupted.
You’ll need to:
- restart DS
- when it prompts for a workspace, choose another (and empty) folder
- import your projects from your old workspace to your new one (File > Import > General > Existing projects into workspace)