I had this problem yesterday, my nightmare. First thing come into my mind is to back all my project files. As I have a lot of branches in TFS for different projects. I’ll share what I did to solve this issue.
1. Backup all projects. It takes a lot of time, but is worth it I think, just in case.
2. remove current workspace and reset the workspace to the current project folder. You can find it here. File -> Source Control -> Advanced -> Workspace.
3. Go to Source Control Explorer and get the latest version of your project.
4. Close the Visual Studio.
5. Go to the project folder in your local PC and replace the projects folder with the one you have backup.
6. Open the project in Visual Studio. All your newly added and uncheck-in files will be inside. Add them back to the project.
* This can be done unless there is no one updated the project in TFS while you are solving this issue, else you have to get latest version after adding your newly added files.