How to connect a HDD hitachi HTS542512k9SA00 to usb IDE 2.5

SOURCE: My PC is not recognizing my WD Passport 120GB USB external drive.

I have the 80GB WD passport and it suddenly stopped working one day.  The unit lights up but nothing else.  Finally I cracked the case open and found, as I suspected, that the drive is simply a SATA laptop drive with a SATA-to-USB conversion card built in.  I suspected that the card was **** so I disconnected it and used a USB hard drive adapter (http://www.tigerdirect.com/applications/category/category_slc.asp?CatId=3770&name=USB_Hard_Drive_Adapter) and I can read/write to the drive just fine.  Best part is that the adapter I use has its own power supply so I'm not pulling juice through the USB cable for a SATA drive. 
Even though mine "works" again I don't recommend these drives to anyone.  They're just not sturdy enough or well designed.

SOURCE: My PC is not recognizing my WD Passport 120GB USB external drive.

Does you drive make any sounds like these? If yes you have a mechanical problem and you should get a specialist to work on it.
If not - try to remove the drive from the enclosure and connect it directly to the computer to recover your files.

SOURCE: My PC is not recognizing my WD Passport 120GB USB external drive.

I had the same issue. Its not a power issue because it shows up in device manager. Heres what I did.

Right-click on my computer and click Manage>Disk Management

Your drive should show up there. Right-click on it. If explore is not grayed out, assign a drive letter to it and you should then be bale to see it in my computer.

In my case explore was grayed out. I had to click on the option to format the drive. After re-formatting the passport explore was available. I then assigned a drive letter to it and I have access again.

I guess somehow using it on multiple computers srcewed up the file-system on it. I was using it between windows and linux.

This fixed my problem.

SOURCE: My PC is not recognizing my WD Passport 120GB USB external drive.

I had a similar problem with my WD passport 320GB. When I connected it to my laptop it never showed up on My Computer even though the blue light on the hard drive came on.
Here is what I did:  Right click on "My Computer" and click on "Manage" and then "Disk Management",. you should see your WD hard drive listed. then click on "change driver letters and paths"  and change it from the listed to another drive. I changed mine from G to F drive and it worked for me.

SOURCE: external hdd not detected in my computer but is in device manager

You probably still need to partition it, before you can even format it.
Try the disk manager in Windows.

In the start menu, right-click "My Computer" and in the popup menu, select "Manage".
One computer management comes up, select disk management and there you should see the disk. You can then create a partition and format it.

Jules