so we can conclude it probably isn't going down for some reason.

Examine another cable end so you understand how the tab locks.

Get a bright light and try to figure out why it isn't moving down.

Got anything else small and pretty flat? Paperclip bent out? Toothpick? Nail file? Hair pin?

The goal would be to push the stuck lock tab down while gently pulling on the cable.

Or. Go to Walmart in Electronics and get a can of
Electric contact spray then turn off computer Spray around the plug in and it should loosen so u can remove it

A small pair of pliers, carefully use them to both depress the tab and extract the plug simultaneously.

Most laptops, it's not a simple matter of removing 'the back'. There are plates screwed down over some components; battery, hard drive/s, memory modules. None of them give you access directly to the motherboard.

Are you trying to do this reaching around the back without pulling the PC out? I think you have to get a clear view of the back, and why not, vacuum everything real good.

Anytime you're dealing with a sticky cat-5 plug, you may want to kind of push it in and shake it a little. You should be able to push the tab down with a little screw driver.

Let us know if that works for you!

Didn't work
going to buy an eyeglass screwdriver.

i tried a small nail file, etc.