[lubuntu] URGENT: Live USB hangs after failed upgrade

So I did something stupid and tried to do the rolling upgrade from Lubuntu 12.10 to 13.04 even though it had been giving me errors and warnings. I think something may have gone wrong with the original (clean) installation of 12.10. #-o

After the upgrade, it wouldn't respond to shut-down commands. When I forced it off, it wouldn't boot up. I get the GRUB menu (version 2.00-7ubuntu11, with options for Ubuntu with Linux 3.5.0-27-generic and 3.5.0-17-generic, both of them regular and recovery mode), but “Ubuntu" and “Advanced options for Ubuntu" just ends up re-booting.

So now I'm trying to re-install 12.10 from the stick (because I stupidly hadn't gotten around to making the live stick of 13.04 yet) and after asking me what language I wanted and after I selected which option I wanted, all I get is the splash screen with the little moving dots.

This happens with both the “Try Lubuntu without installing" and the “Install Lubuntu" options. “Check disc for defects" works. It reports “errors found in 1 files!" and reboots as it promises to when any key is pressed. (I do so love the helpful detail it provides!)

I need help! Lots of it. I can understand the system being hosed, but why isn't the live USB working? :cry: