What happened to my music after the iPhone update?

I have had an iPhone since 4. I uploaded the majority of my cds using PCs to my iTunes account. Unfortunately, those pc's have died.

I went to play music today and discovered ALL the cds that I had previously uploaded to my account are GONE.

They also do NOT show up in the iTunes on my mac.

How do I upload my cds back to my phone?

[Re-Titled by Moderator]