I moved my potted hostas from outdoors inside about 3 weeks ago. They were lush and green when on the shaded porch. But now the leaves are turning yellow and wilting. the plants look like they are rapidly dying. What can I do to save these plants? It's cold outside so I can't put them back out.

Thanks,

Hostas are perennials which need a cold winter period outside, they will come back in the spring/early summer when the temperatures warm.
If the pot you have your hostas in can take the cold winter (clay pots can break from cold) set them back outside where they were growing well before.