Hmm...doesn't have an O/S? Ok, but as far as testing from another machine--what are you trying to test?
The hard drive? Just plug it in on your working machine.
Memory? Find a computer with the same type (SD, DDR SD, DDR SD2), and swap it out.
CPU? Well, if it lets you install the O/S, or part way, you're probably in good shape.
Graphics? Meh, same?
When reinstalling, did you completely reformat the HDD? Reset the BIOS to default? Install the latest BIOS updates?
I can tell you from my troubles in the past, the PC kept resetting randomly, and occasionally freezing--it turned out to be the motherboard. Guess it was the soldering points coming a little lose, or something alike...probably not the case, however.
So...basically I'm saying, what do you expect this "diagnostics" program...to diagnose?