If you have the bars and no 3g signal (the 3g with the orange and green arrows) next to it the market wont work. You have appeared to have lost connectivity and need to either wait for it to come back, turn wifi on and off, turn airplane mode on and off, or use fresh network pro as I do. I've added screenshots to show the phone without the the 3g and how the market doesn't work and then a screenshot with the 3g back and the market working. Good luck hope that this helps.