pc computer used under $500.00 for music only

Try to look to AM1 processors from AMD. Very power efficient. Get a small ITX case with built in power supply (power brick). It's enough to power it up and dead silent. For extra silence you can go for and SSD instead of HDD. 500$ is more than enough for new computer, not used.

A used Oct. 2009 Mac Mini is the ticket. Buy it on ebay for $375 with wireless keyboard , mouse and OS CDROM disk. Upgrade it with 16 gigs DRAM and a SSD from otherworldcomputing.com. Beats virtually all servers on the market if you supply DC power from a linear 18.5V supply. use Amarra playback software. I have won several best of shows using this configuration.

Steve N.
Empirical Audio

Try to look to AM1 processors from AMD. Very power efficient. Get a small ITX case with built in power supply (power brick). It's enough to power it up and dead silent. For extra silence you can go for and SSD instead of HDD. 500$ is more than enough for new computer, not used.

Been posting this a bit today.  How about a Raspberry Pi3 with HiFiBerry and Kodi or OSMC?

A Mac Mini, pre 2013. Mechanically they are well built and have a very long life span. If you don’t care for Mac’s operating system, you can load Windows or Linux, as long as the MM has intel inside. The older MM’s have tons of tweaks available which improve performance and most can be performed by the end user, thanks to online DIY videos.