Server Backup Methods? Losing Files.

Our server is currently losing files on user accounts, seemingly at
random,
and it's utilization, which is usually 5-15% stays constantly at
80-95%. We
are going to try to do a backup to the system but are unsure of a
method to
accomplish this, as we have never considered it before.
Any help to the missing files or ideas on how to backup about 10 Gigs
of
data without tape drives would be appreciated.

Anthony Warren
Computer Technician
Midway High School