I just created a disaster I would not have thought possible. I used a USB stick to install Ubuntu 12.04 LTS alongside Windows 7 on a Dell Inspiron 560.
The install went well, except that GRUB didn't install. No problem; I rebooted to the USB stick and followed the procedure to reinstall GRUB.
Upon my next boot, I got the GRUB menu and could select Ubuntu or Windows (yay!) but Ubuntu locked up during boot (boo!)
The problem is, now rebooting achieves nothing: The Dell Logo screen doesn't appear, so I have no access to boot options, and GRUB never appears. I can't get into the Setup screen, I can't select a different boot device -- nothing! There's no video signal at all upon boot, according to my monitor.
How could a failed boot of Ubuntu cause my computer to refuse to ever output video?