Second SATA hard drive suddenly gone - Win 7

Hello,

I'm currently running windows 7 pro and had no problems with my secondary SATA drive (500gb WD)--it's worked for months. Suddenly, it's disappeared and I have no idea what changes were made to the system that could have affected it. I've looked through many of the threads listed on various forums for help, but to no avail.

It does not show up in device manager or disk management and I know the drive is good (I can use it no problem in a SATA dock). I've even swapped in a new 1TB WD drive which worked for a day and then has suddenly disappeared as well, so it definitely doesn't seem to be a drive issue. BIOS recognizes the secondary drive (both the 500gb and the 1tb drive) every time I reboot, but it doesn't get seen by windows. A previous symptom was a very long boot time--not sure if that's relevant.

Both drives have data on them so it's not as if they're not formatted or have been partitioned properly. Any help would be appreciated. Thanks.