What happens if you play a blu-ray disc(on a blu-ray player ) on a SD TV? Does it still play but in SD or it doesn't play at all?

Well, I tried to feed a signal that was over the resolution of the TV once, and it didn't work. However, if you feed the TV a 480 signal, you'll be fine. It obviously won't play in high definition since you're playing it on a standard def set, but you can still watch them on an SD-TV. Unless the older DVD transfer of any film available on Blu-ray is really bad, you won't really be seeing a difference on your SD-TV.