Lost data and drive detecting when trying to use my book Essential as internal NEED HELP PLEASE

i have a 1tb My book essential drive i bought last year. i got sick of the slow speeds of USB 2.0 so i thought i would just use the drive as a internal drive. i took the thing apart and took the HDD and connected it to my computer with a sata cable but when i booted into windows the drive was not being shown. I’m spazzing out cause i need the data that was on the drive. 

well i took the drive and put it back together and i still get the same issue. not being detected. when the drive was connected with sata it would show up with disk management BUT it it showed 900 gigs of  unallocated space??? when i put it back to the usb config (how it was) and its not even showing in the disk management under windows 7

Is there a proprietary driver that wont allot this drive to be used as an internal drive? how can i recover this drive, i can’t loose the info on that drive.  Please help 

My computer specs are

intel core i7 920 at 3.8ghz

6gb corsair ddr3 1600mhz

evga X58 sli motherboard

Evga 480gtx

Corsair F120 SSD

WD blue 500gb (7200 rpm) Internal (for music  and videos)

windows 7 64bit