Problems with fragmented indexes in SQL 2005

I have a SQL 2005 server where the indexes are very fragmented. When I query one of the databases with the command "sys.dm_db_index_physical_stats", I get an output that tells me that many of the indexes are very fragmented (some are as high as 99 %).. I try to rebuild the indexes, and then run the query again, but the values are still the same.. How can I fix this ? Why doesnt the rebuild of the indexes work ? I have tried several methodes for rebuilding the indexes, but no luck..

Please help !!