If you are connecting a mic, through a mic port, then it wouldn't effect the speakers. Mic is input, speakers are output.
Now if you are connecting a headset, which is input/output, that is different. It is going to depend on how you are connecting it. If it is a single jack headset, then is it being plugged into an input/output port? Or is it just a singular one (say input only). If it is singular, again, it will only let the mic work. Just like if it was input only, then only the earpieces would work and not the mic.
If that is the case, you would need a 3.5mm to USB adapter which would allow you to plug your input/output headset in through the USB which then will work fine.
If there is something different than the above going on, then be sure to post a response to this thread.