Welcome to 2CarPros.
With the engine off, can you shift to any gear? Is there a grinding with the engine on?
If you are able to shift with the engine off, the clutch isn't disengaging the transmission. Most likely, if this happened all at once, is either the clutch master cylinder or slave cylinder has failed.
Take a look through this link:
https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all
If that isn't the issue and you can't shift even with the engine off, it is most likely related to the shift linkage.
Let me know which of those fits what is happening.
Take care,
Joe
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Tuesday, July 16th, 2019 AT 9:22 PM