Which of these two hard drives are failing?

Hi all,

Recently I have been having hard drives problem, and I would really appreciate your help on this.

A few weeks ago, when I booted up my computer, I had an error message at the bios startup screen (something like "SATA1 hard drive error. Press F1 to continue"). The SATA1 drive was my primary hard drive, while my secondary drive seemed to be fine. I played around my SATA cables, power cables, etc. and got to a point when my primary was not auto-detected while my secondary was always auto-detected in bios startup. I then disconnected my secondary, and tried booting up with my primary quite a few times using diff cables, removing rams, changing graphics card, etc. and the primary started to boot once in a few times and now it is working perfectly booting up everytime. I restored my computer to original configuration (with the gfx card, etc., but continued to disconnect my secondary), and decided that my primary hard drive needs replacement. I thought that this may be the last few times I can boot my primary.

Now, my replacement hard drive came, and when I tried booting up with my secondary hard drive, the secondary hard drive fails to be auto-detected in bios startup. I tried different configurations with cables, etc. again, and it has so far never been auto-detected. However, for some reason my primary is working perfectly. I am now at a loss at what is going on with the two hard drives.

I've tried putting my secondary hard drive on another computer and it isn't auto-detected either. The only thing is that few weeks ago it was fine, and after leaving it alone for a few weeks it is not auto-detected.

I would be very grateful for any help.

My hard drives are
Primary: A basic 2007 western digital 500gb
Secondary: A 2010 western digital 1tb green
Mobo: Asus P5b