Most SSDs come in 2.5" sizes while the standard hard drive bay is 3.5". So you need an adapter or other creative means of mounting your SSD. Let's see what you've got.
I mounted not an SSD, but a 2.5" drive in my case. Take a look at this picture; it's on the right side where the stabilizers for full-length PCI cards are. The rails are just the right distance apart to put screws through the holes for the plastic thingies into the tapped holes on the bottom of the drive.
My real SSD will take a little more ingenuity to mount in my new case; I'll be sure to post pictures when I figure that out.