Start your back workout by stretching the lats. Stretch them slow and easy, but pull them as much as you can tolerate. Sometimes a chinning bar works, but grabbing a stationary handle (maybe on a pulley machine) at waist heighth or higher will help you get the leverage you need to get a good stretch.
Once the lactic acid starts building, you will be better able to identify just exactly where the lats insertion points and origin are. Once you feel like you have that "mind/muscle" thingy goin on, you can start with some one-armed pulley rows (alternate sides) with a light weight. Use high reps so that you get a good pump goin on. Keep going. Once you feel like you are really getting somewhere, go back and stretch again.
When you have truly isolated the lats as much as possible and can feel them working (burning like hell), grab a moderately heavy barbell and start your rowing. If your lats do not start burning like they did during the stretches and the high-rep rows, let me know. I think this will solve the problem.
Chances are you are: 1) Using to heavy a weight, 2) using bad form, 3) not really identifying the lat muscles.
As time goes on, you should be able to use the heavier weights and make the exercise more effective.

