This is an occurrence of bug #482757. I've just wasted a day solving this, so I am posting here in the hope that it'll save others the hassle.

On a Dell machine, the included software Dell DataSafe Local Backup (DDSLB) seems to mess up GRUB. When that happens, booting results in GRUB showing the following error message:

Grub loading. The symbol 'X' not found. Aborted.
And for X above, a random string of characters is displayed.

The only fix I have found is the following:
1. re-install GRUB from a live CD to be able to boot up again
2. boot into Windows and uninstall DDSLB
... this will once again have messed up GRUB
3. re-install once again GRUB from a live CD. That solved it for me.

To do steps 1 and 3, i.e. re-installing GRUB from a live CD, the method 3 described here worked fine for me:
Note only "METHOD 3 - CHROOT" for re-installing GRUB worked for me. Find it on the aforementioned page.

(I'm on a Dell Studio 1747, with Karmic as well as Win 7 home pro)