How can i lose weight?

I ve been doin cardio exercise 5 times a week i do 45 mins of treadmill n 15 mins of elliptical trainer.Cant do weights as i dont have a instructor its an appartmebt gym.i did lose 7 kgs.The last reduction in my weight was in june 2007 n since thn my weight has been constant .my diet is also normal but weight is just nt ready to go down.wat can i do to lose more weight as i knw my body has reached a plateau.