I did my Benq the same way, without realizing there's a soft flash technique out there.
But I have soldering skills, so I didn't mess up.
Anyway, I've found that it is EASY, very EASY to bridge the ground and power lines when you cut those traces. The thin traces you are cutting are positive power lines while the ground plane surrounds them. It is easy to remove the solder mask from the surrounding ground plane and when you solder the wires on, you may bridge the contacts.
It might not be dead yet, so double and triple check the area around your soldering, using a magnifying glass if possible, to see if you bridge the ground plane to the power line. Rework this and you should be good to go.
The drive and the 360 is surprisingly resilient to things like this - I plugged in my drive power cable inverted (why they didn't notch it properly is another question) and the console RRoDed, but the everything was fine when I discovered my error (gave me hell of a heart burn though).