My Nokia Lumia 520 show ''unable to find bootable option''?

[Windows Central Question]

my nokia lumia 520 show ''unable to find bootable option''?? please help me

sir,my nokia lumia 520 show ''unable to find bootable option''??

i try windows recovery tools ...."but it shows error unable to sign in the device '' softwere not installed....
please sir....
help me

please help me