How do I fix my hard drive?

Something probably disconnected. Take it apart, check things out and put it back together.

Side Note: This does NOT work with people, don’t try this, the cops don’t like it.

That’s the first thing I did. I mean SATA drives are only one cable, right?

There’s the power cable too.

It’s probably a loose connection – those SATA connectors are really finnicky.

power cable? I can’t find anything that fits… is it separate from what comes out of the power supply?

There are two cables. One that goes to the motherboard, one that goes to your power supply (or rather, comes from your power supply).
Some old SATA harddrives have the 4-pin molex for power (here’s a pic, for reference, of a 4-pin molex)
Most SATA harddrives have a different power connector though. It’s mostly flat. (here’s one of those, for reference)
If you look on your harddrive in a well-lit place, you should see clearly what you need. Unless your power supply is ancient, it will have at least 2 SATA power connectors.
although, if you only swapped your case, and no other hardware, that should not be an issue.

After reviewing the hard drive, it seems like I’m rocking a sata 2 drive. Also that mostly flat connector, the second link you sent, is what I have connected. nothing else.

I swapped power supplies too

It seems I am missing any sort of power to the hard drive. thankfully theres a 4 pin molex converter. will buy soon.

How did the drive work in your old case then? Either your old case had the Molex->SATA adapter or your old case’s PSU had SATA plugs.

Also, the two SATA connectors look quite similar, differing only in width.