What would cause my car to not accelerate after stopping ? but stay running ? PLEASE HELP?

i stopped at a red light and the car stayed running , as it turned green i hit the gas but the car wouldnt move so i turned off the car and turned it back on and it started working normal. ? what could it be causing it to do this... could it have anything to do with trasmition fluid or engine coolant? any type of liquid. i recently added water to the engine coolant.. or wat i thought was now im fretting it wasnt?