If you have a stock nanadroid from when you bought he phone back up your current setup. Flash the nanadroid, boot into the phone and see if qpst will read the phone. If not boot to recovery, then try powered off.
Also on your computer in device manager select ports, then the lg serial port connection. Right click go to properties. then select port settings then on that menu click on advanced. Change the port to 1 or 2. That sometimes is the issue qpst will not read the phone on any other port besides 1 or 2.
If all this fails, the sticky from mmarz has a link to the xionia CWM port. Flash that and try accessing via that recovery.