disk0s2: I/O error -- Gray Screen Stuck

You tried to boot into safe mode w/ verbose startup?

disk0s2 is your first partition after the EFI space. It most likely is your main Mac OS X partition.
The I/O error means it cannot communicate with that partition.
I'd say it's a hard drive failure. Try throwing that drive in the freezer for an hour and plugging it back in.

If you wanna make sure, boot into your Mac OS X install media and verify your disk with Disk Utility. Also make sure your S.M.A.R.T. status has been verified; if it's not, then it's most likely damaged.