Just to add to William's great advise: The power cable has onle one way of fitting in... if you take the power cable and look at it you will notice that the edges of the connecter are belvelled (well the connector is not perfectly square, because it's edges are curved on the top edges). So there is onle one way that you can put in the power cable (and the IDE cable for that matter).

Basically, if it goes in properly, you've connected it properly...
(sorry if I'm wrong here, William might be right but when I fixed a DVD burner for my friend, I noticed that the only way you can connect all the wires to the drive is the correct way)