I recently bought a second hand desktop. I was trying to remove the video card (it's a Gigabyte 560 Ti) and couldn't remove the molex cables (it looks like to 6 pin cables.) I can see that I'm pushing down on the release mechanism and that's it's not trapped, it just won't budge. I was pulling pretty hard and though I might damage it if I pulled any harder.
I've never build a desktop before so my apologies if it's something simple.