Server Help Erchius Mining Facility Multiplayer Bug

I'm sorry if this is the wrong board to put this in, but this is driving us both nuts. This has been an issue since we bought the game in July and so far, I haven't been able to find any threads that actually get it fixed.
My husband and I are tying to do the Erchius Mining Facility Quest together, and all is fine (minus some small lag issues), until the second phase of the Bossfight. His computer freezes entirely and he has to log out to get the game to stop. Every single time this happens, modded or unmodded. We've installed fixes for it via FPS mods and everything, but nothing works. Many think it's his computer, because it's got some rather old hardware, but it doesn't throw any other issues with any other game. He's run Skyrim and several others fine (accept Minecraft. He can't even hardly run that)

Does anyone have any ideas? We're fresh out of them and this is getting beyond frustrating