without more details, all we can do is guess.
the most likely culprit is you have databases that have the recovery model set to FULL, but are failing to take regular log backups.
AS soon as you take your first FULL backup of a database in FULL recovery, the log will grow, until you run out of disk space, OR you take a log backup.
now there could be lots of other things eating up drive space, but that's a common issue that it should be looked at first.
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