I've been trying to find an answer to my problem all day with no luck.
I tried installing windows 7 via bootcamp this morning. I accidentally created the partition before creating a bootable usb drive with the copy of windows 7 on it. Now when I boot up my mac, it goes to an empty grey screen then goes into the "no bootable device" screen. I have tried pressing and holding option once I power on the laptop but that still takes me to the same "no bootable device" screen. I am currently in the process of creating an EFI bootable usb and hoping that this will work.
Is there something I haven't tried yet?