Ipod charges but refuses to sync data to computer

[Something21]

i have an ipod classic 3rd gen that i replaced the battery on and it worked fine but i went to sync it to my computer windows and mac says i need to format the drive before i can use it but it boots the stock OS fine and boots RockBox fine i can browse files and play games fine what is the deal i've tried taking it apart 4 times to re connect the hard drive and battery tried the stock battery again still does the same thing. is there a way i could bypass that ive even tried disk mode. im at a brick wall right now all i wanted is to use my ipod for longer music and game playing time and this is what i get? i forgot to mention that im not using a compact flash im using the stock hard drive and in diagnostics mode the HDD gets a pass i just dont understand what is happening anymore.