Unfortunately it is very possible. PSUs are the component everyone forgets about until it nukes your system.
Download Data Life Guard Diagnostics from WD and/or SeaTools from Seagate (the bootable CDROM version, not the Windows version) and run all the diagnostics. I prefer SeaTools, and I've had SeaTools work on my WDs before, so might be worth trying. None the less, they have their respective tools.
I will say though, if you're sure that the BIOS isnt' seeing them, the diagnostics wont either. But it's worth a try at this point, because they sound like they might be fried.
Can you hear them spin up when you power on?