external hard drive help needed ASAP!

[2fast4u]

i bout an external case and i put my own hard drive in it and it worked when i plugged it in. but as soon as i shut it off and then turn it back on the computer doesn't recognize it. then i turned it off and unplugged the usb and power cable and then plugged them back in and it worked..then i shut it off later on and turned it on and it did the same thing.. i redid the steps and it worked.. then i shut it off and turned it on and then i tried the same steps but it still isn't working now... i had to always go to disk managment and activate it but when i go there, it's not showing up.. what do i do with this thing? this is wut it looks like http://cgi.ebay.com/NEW-3-5-USB-2-0...br /> ZViewItem