External HD not showing up in disk utility or finder even though the HD lights up and vibrates

So a while back I was trying to format my HD so I could back up my computer and watch movies etc. When i finished formatting it I tried plugging it in to the usb port but it didn't show up on my desktop, since it sometimes does this i went to disk utility to see if something was wrong but the only HD that showed up was my internal. Could someone please help me out with this because i really don't feel like buying a new hard drive