I installed a GeForce 210 in my HPa1710n computer with a Win 7 Home upgrade, hoping to connect my TV as a second monitor with the HDMI connector. It worked fine until I tried to use my speakers with the TV turned off. My onboard sound was not recognized as a device. I rebooted and enabled onboard sound through the BIOS and it recognized it again, but when I tried to disable onboard sound to listen to the TV, it disappeared again. Any suggestions on what I'm doing wrong?
Have you checked your Device Manager for a badly installed device?
I'm a little out of my depth here, but it may be possible the two devices are trying to use the same computer resources like memory addresses.
Disconnect all external sound oriented devices, then delete the Sound device in the Device Manager and reboot.
This would cause Windows to reinstall the device.
What sound device does Windows reinstall without your external device connected?