Gray screen immediately upon boot. Cannot enter into safe mode, and cannot show boot loader with the Alt key. How the problem came to be: 


I wanted to dual boot Debian on my MacBook Pro 8,1. I got my USB ready, downloaded ISO, and installed rEFInd. I restarted to make sure the new boot manager worked. It did. 
To burn the ISO on my USB, I followed the instructions on the official Debian page, which require the dd command. 
However I was careless in my typing, and instead of choosing my USB to load the iso to, I chose a 10GB partition that I had set up long ago (i.e. of=/path/to/10GBPartition instead of of=/path/to/USB ). Tragically, I restarted my computer right as I realized what I had done. 


Now, my computer loads immediately into a gray screen, and stays there. The screen comes up just about a second after the boot chime sound. I tried SHIFT, ALT, SHIFT+CMD+V, and I even tried inserting my OS X Lion CD, but absolutely nothing works. It simply goes straight to a gray screen, with nothing on. Any ideas on how to salvage this system? 

Thanks for any and all help.
You could also try holding command-R to start up in recovery mode, option-command-R to start up in Internet recovery mode, or command-S to start up in Internet recovery mode. Or try using Recovery Disk Assistant to create a recovery partition on an external disk.

If you can somehow start up from the recovery system, one thing you can try is to choose the Reinstall OS X option. It downloads and installs a new copy of OS X over your existing installation and keeps user files and settings in place. It fixed a problem I had where my Mac got stuck during the startup process. (I don't remember what part it was though, and I was able to start up in single user mode and from the recovery partition.)

If nothing else works, you could try replacing the hard drive with an empty drive. Since your Mac has firmware support for Internet recovery mode, it would normally start downloading a disk image for the recovery system from Apple's servers, and then allow you to install a new copy of OS X on the empty drive.