It sounds like the download of the operating system is corrupted, so it can't load properly. So now you have the "?" which means that an OS can not be found at start up. I suggest that you restart your computer in the internet recovery mode and hold down the following keys: Command - Option - R. Then allow it to reload the installer. One note of caution before you do this. Download corruption often occurs when attempting a download via wi fi. It's just too much data, apparently. So, if you can, use a wired connection to your router to ensure a clean download. If necessary, temporarily move your computer to set up the wired connection. If that's not feasible, then be aware that using the wi fi method may take several downloads before you get a clean one that works. Good luck.