I recently wiped my hard drive and upgraded to windows 7. I reinstalled GPO (still need to look up my account info to fully register it) and have tried playing around with it.
I use it as a DXi plugin in FL Studio 9. When I go to play a song using GPO's strings, I can hear all the normal FL Studio sounds, and I can see the lights flashing that indicate the GPO instruments are creating sound. However, I cannot actually physically hear any sound coming from the plugin.
I then tried to see if the standalone GPO player works. It does the same thing as a plugin inside FL Studio; although the lights register an output, I do not hear any noise from my speakers.
I messed around with the "Setup" options and finally found a setting that worked:
Sample Rate: 192000
Output Device: MME Speakers (Realtek High Definition)
Output Latency: 43 ms
Okay, good. But as a plugin in FL Studio, there is no convenient "setup" tab that lists these options, and I can't find an equivalent settings.
As a plugin, GPO shouldn't care what the driver settings are--it latches to the host's settings. Unlike a lot of stock instruments, GPO is mod-wheel sensitive. Have you tried moving the modwheel of your keyboard or inserting some CC1 data into a recorded sequence?