the best way is to put the private key on secure hardware and back up the flash disk which is used to put your private key only. and when accessing your wallet, you must be very careful and double-check the wallet site if you are not using a hardware wallet

1. I have hard disk never used, When I try to use and connect to PC, my hard disk warn me to format it, I can't open my harddisk and lost my data.
you have to read this https://superuser.com/questions/284427/how-much-time-until-an-unused-hard-drive-loses-its-data