My suggestion is to uninstall all the drivers and also qgorund control/ mission planner. Then reinstall mission planner or qgroundcontrol as the driver is installed as part of the GCS installation. Then once you connect your PH2 it should pick it up.
When you tested on a different PC did you install teh drivers first? As if you installed the same driver file on both PC then it might be a driver issue (hopefully) otherwise it could be a faulty device, but in our experience we have had no devices fail this way and have been selling PH2 for a long time now, to be honest PH2 board almost never have any hardware failures under normal use as the factory does a great job at QC and using top grade parts.
But if it is the worst case a hardware failure it should be covered under warranty.