install:

Uninstall SourceTree (if it shows on the App&Features list)
Backup then delete the directory below before proceeding with next step
Navigate to C:\Users\\AppData\Local and delete SourceTree & SourceTree-Settings folder
Navigate to C:\Users\\AppData\Local\Atlassian and delete all SourceTree Files/Folder.Download SourceTree and install it.
Download SourceTree and install it.