I would lift it from the pot and check the roots to make sure there is nothing wrong there. If the roots look okay, re-pot the plant in well draining potting mix and give the plant a good soaking to settle it in the new soil. Make sure the plant has good drainage and will not sit in water. You can add a 1/4 strength fertilizer to the water. When it starts to revive and grow, give it a mild fertilizer every 2 to 3 weeks.
As for the leaves, you might trim away the dead part and place the plant in bright light (not direct sun)
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