Interesting... I've never used the rescue disk myself, since I use a linux distro anyway, I always ran the program from my OS.
You can load the backup romfs by holding the Y button on bootup.
Pressing A on bootup should show error messages.
Could you disclose what steps you took, and options taken while using the rescue disc?
What kind of PC are you using? Perhaps use a USB2.0 port instead of 3.0; or a different hub?
You may also be able to remove the microsd from the GCW, and flash it in Windows, see here