You don't want to keep it too wet, especially in winter when it slows down in growth. So, ensure the soil dries out somewhat in between waterings and water moderately, not soggy, at least in winter.

Also, it could just be "adjusting" to it's new light conditions, sometimes the older leaves will yellow and die. Is the center leaf at the top of the plant healthy and green and still growing?

They are pretty adaptable. I dug my musa basjoo out of the garden, plunked it into a pot (with potting soil) kept it in a dark shed for about a month (weather was cool but not below freezing) and now have it inside by the window. I was going to store it in a cool dark spot (indoors) for winter, but realized I don't really have one and will grow it as a houseplant. Anyways, it's hanging in there, growing a bit, but I think the key is not to over water in winter when it's not growing much.

Another thing to possibly check is the underside of the leaves. If it has bugs (spider mites) it might be causing problems and the yellowing of the leaves.

Good Luck,
Glen

Cut back on the watering the soil...and start misting the leaves. Sounds like you might have spider mites - very common due to the dry air indoors especially when a furnace is on. Clip the dead leaves, get a small mister/spray bottle and add a drop of liquid soap, spray often and that should help.