One of my ram slot is bad/cannot be used

Before i cannot use both of the memory slot, i used 2 x 8GB memory module.

But one day, when I try to open a video file from my external HDD, my MBP were lagging/cannot play the video then freeze. I cannot do anything about it. I hold the power button to turned it off. when I turned it on again, my mbp started beeping. I tried to check it. when I use both of the ram slot, it’s still beeping. but when I only use the bottom slot it boot normally. there’s no problem with the ram module, all worked on the bottom slot. when I use the upper ram slot only, it beeps. I can’t use the upper ram slot.

now, I only have 1 bottom ram slot worked.

and my mbp is in higher temp right now. around 80+ degree C, with only 2 safari tabs running

what can I do to my mbp? thanks