Recheck all your wires and see if there are any bridges or dry joints. If there are, redo them. As long as you tried different media other than Princo DVD-R and it still isn't working, then I suspect you may have some wiring problems.
EDIT: In response to your edit, you should ALWAYS solder where the diagrams tell you - they say to do it there for a reason. As for multimeters, always check there is continuity between the solder point, and the pad, and then from pad to Power and Pad to GND. It's pretty fool proof this way
Another tip is to keep GND as short as possible. Have you got a picture of the install?