Do you know the name of the bamboo? You may find it from a specialist bamboo website.
Personally, i'd recommend a clumping bamboo, then you can plant it in the ground. Most bamboos like plenty of water while they are growing and to be on the dry side of moist thru winter.
If it's in a non-perforated pot, does that mean there are no drainage holes? In this case it is probably too wet inside the pot. As the plant isn't growing, the water in the pot will not be getting transpired out thru the leaves and it won't have enough drainage either. So it may be drowning. Is this a possibility?
I'd suggest you look at replacing it with a clumping bamboo though. They are easily maintained, many are edible and they are non invasive. There is a huge variety to choose from. I have 3 types, 1 is 25 metres and 4metres in diameter, or will be at full size. Another is good for 6-8 metres and 2 metres wide and has yellow striping. It cascades and glistens in the sun after a heavy dew. The third stays under 2 metres and is perfect for pots.
Here's an Australian website to give you an idea of what's available.
http://www.bambooworld.com.au/frameset.htm

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The secret is the soil.

IS it in reasonable drainage? They don't like too much water when it's not in the growing season. Did it get enough water when you transplanted? Is the soil you planted into similar to what you took it out of? It may be transplant shock. If it's not overly wet, a drink of seaweed juice helps plants settle after transplanting.

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The secret is the soil.

Make sure the water is getting to the root system. If the soil was not prepared well, it may be water repellant and while you may put lots of water on it, it can drain away without getting to the roots. MAybe dig down and have a look. If it appears to be dry, you'll need to really soak the area. It shouldn't be too late. You could cut back some of the growth too. This will minimise the moisture loss thru the leaves. The seaweed stuff will help regardless.

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The secret is the soil.