2008 Mac Pro w/o Hard Drive - How do I install a new one?
Someone may come up with a better solution than this, but I've never found one in 9 years of owning an 08 Mac Pro...

Though, first of all, it cannot run Sierra, so you'll need El Capitan or older.

Your choices are:-


Get a boot image onto a spare hard drive in the same way you got it onto a USB stick &amp; boot from that.
Get a bootable CD/DVD of Lion &amp; work from there.


or I suppose a late 3  


Take it to an Apple Store &amp; they'll do it for you.


I have never been able to get an 08 to boot from a USB stick, no matter what I've tried. The 09's will, but not the 08's.

It's also too old to boot to Internet Recovery.