MacBook shows circle with line through on boot even on Safe Mode and kernel panics I was rebooting my early 2011 MacBook to run a hardware test on system boot using the shift key. It all went well and the hardware test was accomplished. I rebooted as usual and I get a circle with a line through it instead of the Apple symbol.

Regardless of whether I am booting in safe mode it doesn't boot.

I did the hard disk check and privilege repair which had some complains of that got fixed.
I can't get the system to run. I don't know what a reinstall from recovery will do to my stuff or the machine. What's lost?

Here's a picture of the kernel panic:
You know the answer already.

For some reason your booth sector got scrambled.

You could try to the reset EFI to see if it helps.


  An EFI (extensible firmware interface) is a set of instructions stored
  in computer memory that act as an interface between computer
  components and the operating system during startup. If you are having
  startup problems or your computer components do not work properly, you
  may be able to solve the problem by resetting the EFI to its default
  settings.


Read more : http://www.ehow.com/how_8007618_reset-efi-chip.html

Reinstalling the OS with CMD-R will only fix the system files and not your files. It depends if you have the Restore on your hard drive or you need to use the Internet recovery.