You know the symbol that’s a circle with a line through it, usually used to show NO, as in NO SMOKING or NO FOOD OR DRINKS or NO GHOSTS? Well, its a hard thing to Google for. Turns out it’s called a “prohibitory sign”.
It’s also the sign you get when you boot OS X and your hard drive has gone to hard drive heaven.
A very very sad sign to see. It means “no bootable os found” and it also means “time to get a new hard drive”. (Note – sometimes it can be fixed by flashing PRAM -reboot and hold apple-option-r-p until you hear two beeps. But if instead you hear your hard drive physically crashing into the walls, I don’t think the pram will do it).