So the other day my Mac Pro froze while just browsing the internet. I had to do a hard restart and the computer will not boot at all now. It hangs up at the Gray Loading screen. It looks like it is loading, and then the spinning circle just freezes and the system never moves from that spot. I've even tried booting to an install disc to run disk utility and such, but it won't even boot to that. It does the same thing and hangs on the gray screen. I feel pretty powerless here not being able to even boot to a DVD/CD. The only other thing that I've noticed is ocassionaly the lower 1/5 of the screen will blip with a horizontal orange bar. I have no idea what is going on, I'm fearful it may be a significant hardware failure and not a bad Hard Drive as I originally suspected. Does anyone have any ideas? Not being able to boot to a dvd is very disheartening. This is a 2007 Mac Pro 8 core 3.0ghz with an Nvidia 8800GT 4 gigs ram.