Why does the processor not work and the fault LED come on?

Check the fault code held in the S6 status register.

Investigate the cause of the fault  and clear the error using RS logics software.

A full list of error codes and possible causes is available in the Rockwell manual “1792-rm001_-en-p” available on the Rockwell website

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1762-rm001_-en-p.pdf

The latest user manuals are also available from this site.