If you have the banana indoors watch for spidermite. Musa basjoo is quite hardy and will come back from the corm if it doesn't freeze. We burlap them, cage them with leaves and use tarps or use bubble-wrap. Cut off older leaves that are brown/yellow and don't worry too much about only having 2 leaves on the plant. Here's a friend's description of winter protection: http://www.tropic.ca/K-L-M-N/Musa Basjoo Winter Protection.h... including a snowman made out of a protected banana. Based on your description it really sounds like they either got nailed from a freeze or they have significant spidermites.