red x on my iPod

If the only place the music existed is the iPod with the dead drive then I'm afraid that has gone. The original hard drives used in iPod classics is, I suspect, no longer made and hard to find. An SD conversion kit is a third party adaptation that lets you use a flash memory card instead. I've not fitted one personally, I just know they exist. Google should help you find one.

tt2

The hard drive has probably failed. See If you see a red X icon on your iPod classic or iPod nano (5th generation or earlier) - Apple Support (archived copy). See iPod Service Pricing - Apple Support. You might want to shop around and/or consider an SD conversion kit to replace the failed drive.

tt2