ERROR 21

Well, that sucked.

I just spent about 1 hour breaking my laptop, and another 3 fixing it. To save you the pain, here's how I broke it, and how I fixed it.

As part of debugging another computer, I installed Ubuntu to an external USB drive, using my laptop. This went fine, and I was able to boot the laptop from the USB drive. I unplugged the drive, and tried to boot my laptop the usual way, which gave rise to the error message:

Grub loading, please wait...
Error 21

Oh well hell.

Anyway, like I said above, to "save you the pain", here's the solution:

1) Boot from an Ubuntu live CD
2) Open up a terminal
3) Type the following:
>> sudo grub
>> find /boot/grub/stage1
4) This will tell you something like "(hd0,2)". Use this information for the next step:
>> root (hd0,2) <------ there is a space between "root" and "(hd0,2)"
>> setup (hd0) <------ again, don't forget the space
>> quit
5) Now reboot. It should be fixed.