So I've got this huge problem... About two weeks ago I'm using my snow leopard partition of my macbook pro and browsing the internet via firefox. My mouse freezes for a second, and then my computer just shuts down. I power back up my macbook pro to find a 'cancel or prohibitory symbol'. Strange thing is I can hold down option and boot into my windows partition no problem I go through all the motions suggested by the apple website, such as resetting the PRAM etc.. Nothing works. Flash forward to today. I finally get a hold of my snow leopard installation disc and boot my macbook with it. I run the disk utility and it finds that my hard drive's good to go. I read online and it seems that the best option would be to install snow leopard again. I decide install it again, but about halfway through the installation, the installation fails and pretty much freezes. I had to shut down the macbook via the power button. Now, whenever i try to boot up my macbook I hear the chime, but nothing happens after that. I am just left with a grey screen. I cannot enter safe mode, single user mode, and when I try to choose the start up disk by holding down option, the arrow pops up to choose which disk to pick, but there are no disks to choose from. Sorry for the long message, but I just wanted to type everything out so there are no misunderstandings. I've got a final on wednesday and I have a good bit of material on the macbook that I need to prepare myself for this test. Any help would be appreciated!