Music, Videos lost after iPad updated to iOS 4.2

I had installed iOS 4.2. After I synced my iPad, there is no music and/or no videos on the device.Here is the solution to missing music, videos etc.* Connect your iPad to the computer. * In the iTunes, backing up and syncing.* Open the contents of your iPad in the leftside window.* Choose a song or video, and play it just briefly, not completely.* Disconnect the iPad. Your music or videos has