Gray Stop sign symbol

Hi there,

My macbook pro with startup is showing the stop sign signal. I did the command R and the menu shows backup mac iOS which i tried and won't load. Then i tried disk utility which won't load. I do have weak internet connection could that affect it not loading? It's rebooted a couple of different times with the loading bar and still shows the stop sign when rebooted. PLEASE HELP! Do i need to get a disk with the IOS system and reload it on there? if so where can i get it and how much will it cost. Thanks :)