It sounds like you are working on Windows and, as Derek has said, CS6 is not supported for Windows 10. What has probably happened, however, relates to the fact that Windows 10 runs automatic updates which many users may not be aware of. After these updates run it is not uncommon that an unsupported version of InDesign which has—despite not being supported—been running on the user's computer will either begin experiencing problems, which did not exist before the update, or cease running altogether. If you want to keep running CS6 on a PC try running it in compatibility mode with Windows 7 or get a used older PC (possibly from eBay) and run CS6 on that.