Can't boot after swapping back to old internal HD

Hello everyone! Thanks in advance.

Basically, about a month ago, I was using my laptop to edit photos. It froze. I had to force hard reboot it. It would take a long time then only display the folder with question mark in the middle. I tried the recommended fixes from this forum and the one on Apple. Nothing. It got to the point where the next attempt would include an OSX disc. So I ordered one and waited for its arrival. Once I tried to boot with the disc, and opened disc utility, there was no sign of my current (500GB) HD. So then I sought out the little tools since I lost mine in my recent move. Once those arrived, I changed my HD back to my original 250GB one (I had changed my own HD, battery, RAM, and glass screen before, all successful) to see if the newer 500GB HD was dead (I had purchased it from a friend about a year ago) or if this was going to be a cable issue or logic board issue.

1. I can not for the life of me get my Snow Leopard disc to eject so it wants to reinstall fresh.

2. Using Disc Utility I can see my older 250GB HD (I couldn't see the newer 500GB drive there before the swap back).

3. I used First Aid through Disc Utility to check the drive. It said it was OK.

4. Still can't eject the Snow Leopard disc, it wants to install.

The goal is to just have it boot normally from this old HD that would be in its exact functional state as it was when I swapped it and took it out a year ago. It has sat safely in an anti-static pocket, in bubble wrap, in an old battery box, on a shelf this entire time so I highly doubt it's a hardware failure. I have a hard time believing the newer drive suddenly failed and caused all this, but it was purchased from an old friend and shipped across the country so it's definitely not impossible. But it worked great for a year than suddenly just....poof....while using it. Strange.

I honestly thought switching to the older HD was going to magically make the thing boot.

So I guess I'm looking for direction.

1. Is there any way for me to eject that Snow Leopard disc when I'm unable to move past the "select language and choose drive for OSX install" stage? By the way, my older 250GB HD is not showing up on that screen to even do the install. I'm guessing it's because there's not enough space since the entire older being of my laptop is still on there.

2. I did try to just use my time machine to install a full backup, the last one, which unfortunately will cause me to lose several photo and media files, but meh....I just need this thing back up and running at this point.

3. Do any of the things I have described point at a dead HD cable? I could order and replace that.

4. Do any of the things I have described point at a dead Logic Board? I really don't want that news...ya know?

What on earth am I missing? I'm not miss computer pro by any means but I'm definitely self sufficient and have never needed to rely on help for any of my problems....so I'm a bit embarrassed to be here asking about this. I've officially used my entire IT knowledge and hope I'm just missing something super obvious that'll make me say "stupid stupid girl" to myself.

Any help is SUPER appreciated!!! **I'm not taking anything in to Apple or looking to purchase a new one**