If your back one works, I beleive it's not your motor. I had this problem on my windshield with 2 washers. What happened was my washers got clogged, i'm guessing it was because I didn't use them very much. Anyways, either your A). Washers or B). your Washer Hose is clogged, which is located under your Hood
up front. What sucks is, if you can't get them unclogged, your going be paying a rediculous amount of money to replace the old washers with new ones.
Just to double check your motor isn't broken, try and spray your windshield and see if just a little bit comes out the front 2 washers. If something comes out, your motor isn't broken.
Hope this helps you out... Good luck!