Different ssd's disconnecting

[kmce]

Hello, I was using Unity and left my PC for a few minutes and when I came back my project had closed down, and was unable to start it again. So I checked my "devices and drives" and noticed the SSD that unity was installed on was not showing. I figured the ssd had failed but wanted to make sure it was all connected properly first. So I opened PC made sure all connections were fine, checked again and the SSD still wasnt showing. I had forgot to screw the sides back in, so shutdown pc again, but upon restarting, the SSD that I thought had failed was showing up, but another SSD that was showing fine before, is now not showing. I am sure all the connection in the case in fine. I have basic knowledge of systems etc, but not enough to diagnose, so hoping someone might have an idea of what is happening. Why different drives seem to be disconnecting?