There’s a known issue with some of the older versions of Plesk, where the domains show 0.00MB in disk usage and bandwidth, despite having several (hundreds) of megabytes worth of storage. The problem usually exists in the statistics program not being run by Plesk as it should be.
There are several possible solutions, which can be tried harmlessly. First is to restart MySQL and PSA (Plesk Server Administrator).
/etc/init.d/mysql restart
/etc/init.d/psa restart
If that does not solve it, you can run the following commands to execute the statistics-tool in Plesk, which will re-calculate all stats (disk & bandwidth usage).
mysql -uadmin -p`cat /etc/psa/.psa.shadow` psa -e"update misc set val='byte’ where param='size_count_type’”
/usr/local/psa/admin/sbin/statistics
This will re-run all the statistics for the domains (and if you have a lot of domains, this can take a while) and Plesk will show correct disk- and bandwidth usage again.