inserted SSD but inactive

Sad to tell you need a different SSD! The SATA I/O of your system is only SATA I (1.5 Gb/s) Most drives today are a fixed speed SATA III (6.0 Gb/s). One of the few drives you can get that will work in your system is a Samsung 860 EVO. Look at the Interface line in the space sheet you’ll see it supports 1.5 Gb/s. What ever drive you get needs to list it like this one.

Now the bad news! Keep in mind this system is unable to support newer more secure OS-X versions and the one you needed that properly supports SSD’s. You need OS-X Yosemite 10.10.x  or newer. I’m not sure if its worth the cost. I would just stick with a cheaper HDD drive (again one that runs at SATA I speed). I also wouldn’t use it online or store any personal info on it either if you are using anything older than OS-X El Capitan 10.11.x.