i have upgraded to the latest upgrade of ios 8.4 after that i was not able to sync music from pc. many of my previous music files are gone. please help me

i have upgraded to the latest upgrade of ios 8.4 after that i was not able to sync music from pc. many of my previous music files are gone.

when i connected my device to itunes through usb, everything works perfectly except the music part. its only shows icloud music sync option. im attaching the screen shot. go through it and please help me.