Everyone's talking about windows MBR, and it does NOTHING. No kidding. Nothing is changed.
If this helps, here's a picture of what I think is going on. (From now, I will document what I do, in case it helps someone, somewhere.)
   
Basically, if I turn on my laptop, BIOS works fine. It then tries to load GRUB 1.5, and returns Error 21 if the USB drive is NOT connected. (Represented by the dotted line)
If the USB is connected, and detected, it goes to GRUB, where I can boot Kubuntu or Windows 7.

I've used a Windows 7 recovery disc (made after I backed everything up) and this...

followed by...

Neither had any effect, and according to the disc, Windows 7 booted fine, generating no errors. thus, I believe the problem lies in which MBR the BIOS looks to.

Shortly, I shall attempt playing with the CMOS startup, in accordance with some person's fix to this problem:

If I make no more posts after this, it likely means I broke my laptop quite thouroughly, and professional help will be sought.

If I vanish, remember me for what I was, not the incredibly stupid thing I did.