KC - you need to either change the boot order in the BIOS (you would anyways) or you should just power it off, open the box and switch the SATA cables from the back of the two different hard drives (it might be easier to trace them back to the mainboard and switch them there).
You could also boot into windows (off C drive).
Then go to start-run, and type in "msconfig"
There is a boot tab, and you can choose which disk to boot from.
If you do it this way rather than just swapping cables, your slow drive will still be the system partition (which is MS's f****ed up way of saying "the drive the system boots from") and the boot partition will be your SSD (which is MS's f****ed up way of saying "operating system drive).
I sent you a pm and I've just sent another with my phone number. You can text me, and I'll walk you through either method.
Don't format until you're sure.
1) Let's find the boot order in your BIOS
2) Let's switch the SATA cables cuz it's the next-easiest way
3) We could go with not changing your config, and have your system point to the 2TB, which then points to the SSD to start. It doesn't mean your SSD won't be C drive, but if your 2TB gets removed then it might piss off your PC (though a copy of your sole drive config IS copied to your SSD at this point).
Gimme a call / text / email.