System info: (will be amended if any more info is asked for)

My laptop runs Xubuntu 12.10. As it has a Solid State Drive, /tmp, /var/tmp, /var/log and /var/log/apt are set to tmpfs in the /etc/fstab file - in case this makes any difference.

Problem

My problem is quite simple. Approximately 50% of boot attempts end in the mouse cursor on a black screen (presumably LightDM failing to load), forcing me to restart and try again. I can access the CTRL+ALT+F1 terminal to reboot the machine, but it's very annoying having to boot and reboot two or three times before one works. Oh, and this problem is the same whether I use the Xubuntu or Unity greeter.

Thanks for any help you can give.