Ubuntu :: Computer Completely Stopped Booting?

So, first of all, this is my sisters computer so I am not sure exactly what happened. I had installed ubuntu alongside WinXp a couple of weeks ago. Today she booted into xp for the first time and accidentally launched some system restore option. A dialog box appeared and told that if she continued, everything on her disk would be erased. apparently, there was no indication of how to not to continue, so she shut it down by holding the power button.

Now, it won't boot. Not even to grub, it just cycles where the screen comes on, a courser blinks in the top left, and then it automatically restarts after about 5 seconds and repeats (unless one launches BIOS configuration). I assume something about the MBR has gotten messed up. I tried booting off a USB thumb drive, but it just accessed the drive for a second or two, and then went back into the cycle (I tried every USB socket, and the BIOS was configured properly to boot off external USB, also, I was able to boot my computer from the USB)

how to proceed if I can't even boot off of USB. Oh, the computer is Asus Eee pc netbook (no CD drive).