You buy ONE and ONLY ONE download. it is your responsibility to move/copy/backup your music.
it has always been very basic to always maintain a backup copy of your computer files/docs/pics/music/etc.
Use your backup copy to put everything back.
If for some reason you have failed to maintain a backup ( not good), then you can transfer itunes purchases from an ipod: File>Transfer Purchases
1: If Windows isn't working:
You need to boot the computer from a "recovery disk or USB" that has a operating system on it and a graphical user interface to transfer files from your boot drive to a external drive.
Burn a ISO of Parted Magic with ImgBurn to a blank cd.
Once you have it done, consult this page for your BIOS boot key to hold to get into the BIOS.
Insert the cd, enter the BIOS and set the cd as the first boot option, reboot off the cd. Hook up the external drive.
Once in PartedMagic, click on the Mount Devices, click mount on the largest storage option, it's likely your Windows partition. Navigate to your files, clcik on Mount Devices again to open another window to your external drive and simply drag and drop copy of files.
2: If the computer hardware isn't working, but the drive might still work:
• You'll have to remove the power cord and manually extract the hard drive. This might result in some damage.
• There is a powered IDE/SATA to USB adapter for sale online for $20 that you can take that internal hard drive and use it like a external drive to access your files from another Windows machine.
3: If your iTunes content is deleted...
• It might be recoverable if it hasn't been overwritten yet by fresh data.
• You need to use undelete software pre-installed before the iTunes content was deleted or while on a bootable cd/USB and a external drive to transfer the recovered files. You can install "undelete" type software on a new/other Windows machine and recover if your using the IDE/SATA to USB adapter.
4: If the hard drive doesn't work and...
• The data isn't worth spending $2000-$3000 in a ATTEMPT at recovery, then your finished
5: If any of the above is beyond you (like brain surgery is for me), then seek professional computer recovery services.
Hope this helps.