Hi,
Is the original partner the template one? if so, you're not suppose to actively work on it. That one is only meant for defining data you want other partners to inherit. For instance, sample content.
If we are NOT talking about the template partner, start by going to MySQL and make sure that the data is there, for example:
mysql> select * from category where partner_id=102;
would return categories that belong to partner ID 102.
If the data exists there, try to reindex Sphinx using:
# /opt/kaltura/bin/kaltura-sphinx-reindex.sh
if it does not, then something happened to the DB and I'm afraid there's not much I can do other than recommend you import from a backup.