The Spirit rover is no longer sending data to Earth. Ground controllers at JPL have been able to confirm that the rover is recieving the data, but there’s no data being sent back other than the confirmation signal. This means that the rover is still powered and able to receieve data, just not send anything. What could be the cause is entirely unknown, and unless the rover can communicate more information about its status it’s nearly impossible to know what happened.
As long as the rover remains operational, there’s hope for recovery. Best of luck to JPL in getting Spirit back on the right path to discovering more of the red planet.