I just had the same issue of not being able to boot. What I did was hit esc as soon as the Asus splash screen appears and then chose the boot device. In my case, I chose the dvd as I went back to 7...

I'm having the same issue myself, the error code I'm getting is 0xc0000521a. I ran check disk, no problems and tried to restore as well. System restore failed,so I tried to just reset and that failed...