My External USB Hard Drive doesn't show in my Vaio E Series

Hello,

I'm just wondering why it happened? and how will I fix it? Actually it was my old Hard drive but its only 320 GB that's why i bought a new one and then replaced it, so after replacing my hard drive I made it as my External USB so that i could still have a benefit to it. At first I connected it to my computer to test if it will still work and to my many thanks it was working and then i formatted it and then due to my excitement..after clearing my hard drive's files i put all my movies in there which if I'm not wrong was 160plus GB in size. Now after i unplugged it, the next day I plugged it again but not working anymore! In any computer! I'm sure it was not virus because my laptop does'nt have any virus and I didn't plugged it to other computer before I plugged it again on mine. I hope that you could help me in my problem. :( I want to know how to fix this and what might happen to this to not working anymore.

P.S!
Sorry for my english/grammar. I'm from Philippines and I'm only 14 years old. So i'm still lacking of english words. kekeke~