Why both of my drives , (mac HD and booted USB drive) are locked ? Cant install os X

I have a Kernel error at startup, so I need to reinstall OS X Lion.

I used MacOS extended journaled and bootable flash drive restored with bootable OS X LION dmg file. But, after booting from Usd i can't reinstall lion because hd is locked. Also i couldn't find a way to unlock it with disk utility.

I dont have a backup of my HD, so i have to reinstall and hope to save my files.

Any help please ?