|Why do you need to unplug the speakers anyway?|
When you plug them back in, make sure you plug them in to the correct jack on the back of your PC. This is usually the one with a light-green bezel. The other two jacks (blue & pink) are for line-in and microphone.
After plugging them back in, you may just need to restart Windows to fix the problem.
If it's already plugged into the correct jack and still no sound after restarting Windows, try re-installing the audio driver which you can download from your PC manufacturer's website, or if it's a soundcard which was not fitted by the PC manufacturer, download the driver from the soundcard manufacturer's website.