Mac Pro Unresponsive

It's an interesting chain of events, so hang in here with me...

First of all, it is my friend's Mac Pro (Perhaps a 2008 or 2009 Model... of course the previous owner scraped off the serial number and the product numbers, so i have no way of checking) and he asked me to take a look at it.

Upon plugging everything in and starting the computer, I got nothing except for the menacing question-mark folder, reminiscent of the Riddler. So, I held down "Option" the next time i started it (To which it displayed two choices, {The main HD "Zakattack", and the Recovery Drive}) I tried both drives and nothing came of either of them, vice more riddles!

Ok, SO... something is fishy. I startup again and attempt to open the disk utility... nothing. And again... Nothing. and another 10 times... Nothing.

Alright then. By this point, I'm trying every single trick in the book, and absolutely nothing will work. So, i physically removed the hard drive and inserted it into my Blac X 5G Hard drive reader. I then partitioned it, reformatted it, even threw Yosemite on there to see if that might help. Wrong. Nothing.

So i made an external drive with a bootable version of Yosemite, and although I could select the drive on startup, I would still be transferred to a never-ending blank screen, or eventually a question-mark folder.

Frankly, I am stumped. Anyone else have any ideas?

I thought maybe if I tried to install an earlier OS... someone told em that the graphics card wont be able to handle this OS. But if i cant even open a graphic interface, how am I supposed to install a new graphics card? Would installing an old operating system even help? And if it would, where would I find one? This one has me a little frustrated...😝