What does the flashing folder mean when I boot my late 2011 Macbook pro?

Hi,

Last night I attempted to put a new hard drive into my late 2011 Macbook Pro. Here is what I did prior to this problem.

I replaced the hard drive and then realized that it was faulty so, because I was running short on time I just put my old one back, connected everything and closed the back of the computer.

When I booted up the computer again I kept getting the flashing folder. I booted in recovery mode and all that I see is

disk0

MacOS Base system to the left.

It will not let me restore, repair, or anything else its all grayed out on the right side of the disk utility.

Since I didn't erase the hard drive my best guess is that this is the hard drive cable issue. Can anyone help with this?