To identify full-text indexes on a server run:
SELECT object_id, OBJECT_NAME(OBJECT_ID) AS ObjectName, is_enabled, has_crawl_completed, crawl_type, crawl_type_desc, * FROM sys.fulltext_indexes
To enable an index run:
ALTER FULLTEXT INDEX ON [ObjectNameHere] ENABLE
To disable an index run:
ALTER FULLTEXT INDEX ON [ObjectNameHere] DISABLE
Note that [ObjectNameHere] should be replaced with the object name identified from the results of the first query.