By default, vB only allows a forum depth of 2 to be dispayed (this includes categories.) To change this:

1. Admin CP -> Options -> vBulletin Options -> Forum Listings Display Options -> Depth of Forums -> Forum Home -> 3

2. Manually create new templates to increase the forums displayed. You have to add template forumhome_forumbit_levelx_post and template forumhome_forumbit_levelx_nopost for each level past 2, replacing the x with the level number. For instance:

forumhome_forumbit_level3_nopost
forumhome_forumbit_level3_post
etc.

Copy the contents of the other templates ('1' or '2') into these new templates. Then change the 'Depth of Forums' setting in the Admin CP to the appropriate number.

Repeat as necessary for whatever depth you want.