How can I tell which HDD died?

[RedDirt]

I was playing with a 'new' toy, a HP Pavilion Elite m9290a that was sitting around for a few years. I noticed the hard drive was a bit noisy running, bit like an old 386, I thought that wasn't abnormal. But then it started doing the click of death. Then soon after slowed to a crawl, then blue screen, with Stop Error. It can't reboot. I've got as far as the same stop error. So I'm just assuming hardware failure. This computer has two 500GB hard drives. How am I now able to tell which one is bad?

 

[Jwpanz]

Unplug one of them and try to boot. If it goes through that same stop error then the one left plugged in is the boot drive.

 

[RedDirt]

Thanks, nice and easy.