That is a kernel panic, which means something in the system is causing the OS to crash. That or a piece of hardware has gone haywire and prevents regular OS functionality, thus causing the kernel panic.
Too many variables too know. I'd be guessing, your best bet is to go to Apple (or call them). Assuming it happens often (or as I understand your issue, always upon start-up).
yes it happens at start up at first it it was showing a grey folder with question mark so I reinstall snow leopard on a external hard drive thinking the other hard drive in the late 2008 MacBook air had crash so when everthing finish installing plug the hard drive up to MacBook air usb and know im getting that black screen of death really need my laptop but its out of warranty so I know apple going to change me to fix it if they could lol
Also the battery is swelling to only can power MacBook on with charger I wonder would apple replace laptop that's out of warranty I read online that this is a common problem