Since BIOS says 2 SATA devices are recognized, there's another thing to try. Unplug the SATA data cable from the WD drive and plug it back it. A poor contact can do weird things like this.
I have a spare WD drive from a Dell that does exactly the same thing. BIOS sees it and then it won't boot 100% of the time. I worked on it for weeks until I finally figured it out. The SATA connections at the drive end were just loose enough to lose full contact. If I took all the tension off the cable it booted. I tightened it up with a very thin piece of plastic (Post-It bookmark) and all issues disappeared.
BTW, it was a used drive and was mostly likely ditched for this very reason. Now it works just fine and passes all tests.
