mysqld is not producing binary log
Things I'd check:


Are any changes happening? Binary log doesn't include SELECT queries, only changes. Compare the timestamp on files like ib_logfile*.
Are replication filters excluding changes being made?
Are sessions making changes while SQL_LOG_BIN=0 is suppressing binary logging, either globally as @RolandoMySQLDBA suggests, or else per session?
Disk is full?
You are looking at binlogs in the wrong directory?