Black screen, charge light shows only initially

A few months ago, my oneplus x bricked for apparently no reason. I went to the bathroom, came back to my desk and my phone was making a hissing sort of sound from the speaker and then went completely black. Since then, it hasn't turned on. When I charge the phone, the charge light only shows for about 5 minutes and then goes off. I can't turn it on no matter how long its been charged/plugged in. My pc also doesn't recognise it (holding down power button + volume down does nothing). I thought the stock battery was dead so I bought a new one; same result. I've also reseated the ribbon/extension cables; same result.

wat do? I'm really lost.

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