Make sure the axis has a clear path of travel. Tools, part fixtures, or workpieces that are too large can crash into the machine enclosure.
Look at the machine's alarm history. Overload alarms followed by over current alarms are a sign of a crash.
Look at the machine enclosure, spindle and tooling for damage. Damage to the tooling, fixtures and enclosure are signs of a crash.
If there are no signs of a crash, inspect the ballscrew and linear guides. They must move or turn freely by hand.