This is not bamboo, but I'll guesstimate that there was something nasty put in the water at some stage. (I too was a student once too)

Try changing the water daily, and hopefully whatever was in the water will gradually be 'leached' out?

Alternatively, if you have a 'good bit' left of the lucky bamboo, then chop it off, and place it in a new pot/vase and it should continue to grow.

If neither of the above help, then I'm afraid you might have to buy another.