WD WD10000H1U-00/10EAVS not being reconised

Hay people, first post and im just needing some help fixing my WD hard drive… its been working but recenting when i plug it into my computer(window 7) it doesn’t load up. but when i go into device manager it shows up( http://i43.tinypic.com/168em88.jpg))
when i plug it into my mac it comes up and when i try to format it it wont allow me.
here are some FIQ answers that iv answerd below.

Does the LED light on?.Yes it is

Does it spin up or making any noise?.It seems to spin up and ventilate.

Does anything thing pop up on the screen? Nothin pops up on my screen but my computer makes a noise(when you connect somthing). but when i go into my folders its not in my computer.

Does the disk manager shown any unknown devices?. No. it actually shows that the device is connected

Have you tried a known good 12V AC adapter?.Have 12v dc power.

]Have you tried a different USB cable? .Have tried a new / different cable.

I AM HAVING THIS SAME ISSUE WITH WINDOWS VISTA PLEASE HELP!!!!!

I HAVE ALSO DONE EVERYTHING THAT THE GUY WHO STARTED THIS THREAD TO HELP TROUBLESHOOT ISSUE