Check your startup server.log for errors relating to the unavailability of the office2html converter.

checked the startup server.log and only appears the same message as informed above.

"org.nuxeo.ecm.core.convert.api.ConverterNotAvailable: Convert office2html is not available."

Are you sure there are no ERROR lines before that?

Follow server.log generated after attempting to preview:

2013-11-05 15:09:47,287 ERROR [org.nuxeo.ecm.platform.preview.restlet.PreviewRestlet] could not build preview for missing blob at default
org.nuxeo.ecm.platform.preview.api.PreviewException: Converter any2pdf is not available

"Converter any2pdf is not available". Are you sure you followed the installation instructions regarding third-part software needed for conversions? Installing and Setting up Related Software

See this log that also appears on startup:

"2013-11-06 10:05:36,278 WARN [org.nuxeo.ecm.platform.convert.ooomanager.OOoManagerComponent] OpenOffice was not found, JOD Converter won't be available: officeHome doesn't exist or is not a directory"

I have installed libreoffice. Is there any configuration file that points to the folder libreoffice?

I use Nuxeo 5.6 for windows.

WARN [org.nuxeo.ecm.platform.convert.ooomanager.OOoManagerComponent] OpenOffice was not found, JOD Converter won't be available: connection failed: 'socket,host=127.0.0.1,port=2003,tcpNoDelay=1'; java.net.ConnectException: Connection refused: connect