I currently have a very similar problem!
Optiplex 755 + new WD My Book 1TB drive. Seen via USB2 but not via 3rd party SATA cable to backplate + eSATA cable to drive. BIOS External SATA set on (this option only appears to be displayed when the drive is connected - does not need to be powered on) ==> drive ID shown as unknown (not sure how significant this is).
Still trying to establish where the problem lies (PC, cables or drive).
I bought an eSATA header to connect to this port. I also enabled it in the BIOS which is latest & last release by Dell of A22
The entire system locks up on boot when an eSATA device is connected. It does not complete BIOS checks.
When I use a real SiL3132CNU eSATA card everything works fine. I'm not exactly sure what's the deal with the internal header but if anyone else who has used this older equipment wants to chime in it would be appreciated.
All of the spam-bot "Pro/Experts" in the forum...just stay quite. None of you add any value to real discussions.