dual thunderbolt displays stopped working

Hi All,

Until last week I had 2 thunderbolts daisy chained to my 13" macbook pro. It worked fine for the last 6 months.

Here are some details:

1. Each display runs individually

2. I've tried reversing the order of the chain with no change (i.e. it doesn't matter which display goes first)

3. Peripherals only work from the first display (the one that turns on)

Any idea what would cause this?

Thanks!