If the content is in iTunes on the new computer it must not have been selected to sync from within iTunes. Connect your iPad to your computer again and go into each iTunes section and select the content that you want to sync.
If you are using the newest version of iTunes and you cannot see your iPad in the sidebar go to View>Show Sidebar at the top of the screen. Once the sidebar is visible, click on your iPad name under the devices heading and the Summary Page should open on the right. Select from the tabs at the top to go into, music, apps, photos, etc.
Sync Your iOS Device with a New Computer Without Losing Data
Syncing to a "New" Computer or replacing a "crashed" Hard Drive