First, I would just double check the voltage and polarity of the supply to the 4th row. This may sound crazy, but we've all made some silly mistakes. I'm only asking so that it can be set aside as a possibility.
Also, put a scope on it to see if it's clean.
Then:
I just tryed the scope method. No luck. The signal is lost at the last led in the 3rd row, but if I connect the out of the second to last led to the first led in the 4th row there is still no light form there onward. I think it is a problem with the power and the data. ![Banging Head |O](https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif)
If you can, disconnect anything and everything from the output of the last LED on the 3rd row - and then check if there is a signal coming out at that point from the chip itself. If you find a signal, then something you had connected to that point was shorting it out. If so, look for shorts - and remember they could be hiding. If you DON'T find a signal then I would suspect an open circuit somewhere - or possibly the signal output of that last functioning LED has been killed somehow.
Clutching at straws - you could then try disconnecting anything and everything from the input to the first LED of the 4th row and then try feeding it with a known good signal.
At this point, I think I would use the scope as a first line of signal detection. Once you get positive indications, then I would start using LEDs.
Or maybe you will work it out yourself. Many a time I (and I'm sure others here) have worked out the answer to a problem by trying to describe it to someone else.