Well, there is another possibility to consider. How many villagers are you trying to support with the farm? If it's more than a dozen, they're probably eating all the food before you even see crops. You really need level 3 of Harvesting if you want to support a higher population.

The way to determine if your farm is actually producing is to check the stats screen. If the food quantity is going up, they are harvesting all of the crops while the game is off. The crop graphic will only appear if there are crops actually on the farm when the game is running. They continue to harvest and eat when the game is off.