I think 1LiquidPC pointed to the problem, but let me suggest what to do about it.
The root of the problem likely is that Windows can only work with ONE audio output device at a time, although you can change which device that is. And 1LiquidPC and I suspect that, up until now, you were using the audio chip on your mobo and plugging speakers into the back panel of your computer.
As he / she said, many video cards now also contain their own audio output chip so they can send sound out on the HDMI port to your monitor or TV. It has become common that, when you install the drivers for your new video card, that installer also installs the drivers for the audio output on the same card and then sets Windows to use it instead of your old choice. So now Windows is using that chip and sending sound out on the HDMI cable. But it you are not using speakers in your monitor, you'd never know that. And of course, if what you really want is to use your speakers and headphones where they used to plug in, having the audio signals on the HDMI cable is useless!
What to do? First, connect your speakers and headphones or whatever they way there used to be. Now in Windows click on Start and choose Control Panel, then Sounds and Audio Devices, and the Audio tab in that window. In the top box there's a drop-down window with an arrow - click that. You'll get a list of audio output devices in your machine. One will be the video card chip from AMD, another will be the mobo audio system possibly from Realtek. Choose the mobo output as your Default Sound Playback Device. Similarly in the second box, you can choose that system again as the Default Sound Recording Device, if you need to. Click on the Apply box at bottom and back out. You should be able to play sounds again as you used to do.