Macbook boot troubleshooting Since a system upgrade my macbook fails to boot properly: a loading bar appears, it takes about 15 minutes to get filled and then the system shuts down again.

When booting in recovery mode, I tried to "Repair" the main partition in the disk utility tool but an error message told me there actually was an issue but it could not be fixed and I needed to format/reinstall the system.

I also tried to erase the bootable partition but it also failed (saying the drive could not be unmounted).

I tried to choose "Reinstall Mac OS X" from the main menu, but my main partition was not found.

I don't have any bootable disk or USB drive of Mac OS X. Is it possible to create one from a windows PC?

What else could I try to fix the problem?
You won't be able to erase the boot disk since you're currently booted into a partition on the same drive (which will result in the unmount failure).

Try Internet Recovery. Boot with ⌘⌥R until you get a spinning globe, then follow the instructions.