macbook pro doesnt find any partitions and doesnt boot from usb

I was playing with the partitions, i used dd command to overwrite one partition to another and i messed up. When my macbook pro starts it doesnt find any partition to boot. Because my dvd drive is broken i created a bootable usb to boot from it. When i boot the computer and press alt button, the bootable device is regognised regular but when i press enter or click on device icon to boot from it, it doesnt happen anything. Please help me.