I don't understand about the screws, part----unless, it's one of those where you just have to screw the screws, IN, more; I've had to do that, more than once.
As for the 15-pin, it may be that you're not seeing the input, cuz it requires a girl or boy plug, instead. If that's the case, you can easily affix an adapter----they're double-headed, so you can turn whatever plug, into whatever other kind of plug, you need:
https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=cable+plug+adapter%2C+motherboard
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White female; age 59; diagnosed Aspie.
I use caps for emphasis----I'm NOT angry or shouting. I use caps like others use italics, underline, or bold.
"What we know is a drop; what we don't know, is an ocean." (Sir Isaac Newton)