I was running Firefox on my macbook (running Mac OS X 10.5.1) when the spinning wheel came up and the application wouldn't force quit so I powered the machine off manually. Since then, when I try to boot, a grey screen appears after the start up chime and nothing else happens. I went through the steps recommended on apple support for this problem, but when I get to the part where it recommends getting to disk utility via the Mac OS X installation disk, the MacIntosh HD is not listed. Does this mean my hard drive has crashed? Does anybody have any ideas or additional steps I can try to get my macbook up and running?