back up for music was on old pc that died, how to download purchased music?

This article should provide you with what you need to download your purchased music:

Download your past purchases - Apple Support

See Recover your iTunes library from your iPod or iOS device if you have any devices. There is also a possibility that media can be extracted from your old computer's hard drive even if the machine itself no longer boots up.

tt2

Do you not have a backup copy of your computer?