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?
Best Answer
If you reset the NVRAM, the Mac should find the first Mac OS bootbale volume and start. If not, you can power down and try the option key again.
If that fails, your Mac boot volume is broken or your hardware is broken. Try booting to Recovery HD or internet recovery at that point to reinstall your Mac OS on top of your old Mac user and data.