[thisistoto]

That doesnt necacerialy (wow bad spelling) mean that it wont work. Just that they wont help you with technical problems.

The main difference is the connection, USB in your case vs. a Serial/IDE connection inside the tower.

Go to your device manager and see if anything is flagged (including the drive when its connected)

I would first try to rule out a bad cable/bad USB slot by using it with something that you know works (ie i duno something)

Do you have automatic updates turned on? The reason why it worked once and not know is because during that time there could of been an update to a driver that doenst recognized the drive anymore.