From the Get-go:
Open the case and check if the HDD is acctualy there!! (it would kinda suck if it wasnt)

if it is, take it out, boot the system, it should beep at you with a simiral error. (if it gives a different error, the HDD might be half-alive)

Plug the HDD in, out of case, check if it runs, you should hear it, it might also have a tiny LED on the bottom of it, encapsulated in glue. If it dosn't work, it's almost safe to say your HDD is fried, but keep going, theres more.

Find a temp-replacement, the other machine will do since their identical machines, see if that one works. If this dosn't work on the machine, but does on the other (live) one, then your Mobo/CPU might also be fried.

I know alot of this might have been mentioned, but here it is in a step-by-step-kinda way.

- Noia