(93 Ford Escort wont shift while started (manual

I have a 93 fors Escort wagon.It has frozen up and wont shift while running.When I turn the engine off it shifts just fine.

Sounds like the clutch is not disengaging. If you put it in gear and start it up, does it move with the clutch depressed? If so, it's probably the clutch slave cylender that is mounted to the transmission.Look behind the rubber boot while someone pushes the clutch - you should see the shaft move back and forth.