When you try to start it is it clicking or making a whirring sound. Whirring indicates its the starter if not as mentioned its your battery or alternator. Try another battery first. When you turn the key before you try to start it can you hear the fuel pump priming? If not that maybe your issue. But honestly if you can get it started and drive it for a bit and then try and start and it wont it will be the alternator or a connection to it or the battery as it should charge the battery as you drive