IPOD CLASSIC WITH RED X CIRCLE

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

See Corrupt iPod Classic - Apple Community. What are your HDD stats? Sometimes when hard drives are at the end of their useful life they will sometimes work for short periods of time.

tt2

How long they last will depend very much on the operating environment. Changes of temperature, high humidity, and mechanical shock all reduce the working life, as does simply using it. 20+ years seems like a good innings.

tt2