I would certainly check to see if there is an updated audio driver for your sound card.. Such updates occasionally fix the issue.. On the other hand, after unplugging the headphones have you tried visiting the Control Panel/Sounds and Audio Devices/Volume tab/Advanced button under Speaker settings, then toggle the drop down menu away from "Desktop speakers", then back to "Desktop speakers" again, then click on "apply", then OK..
Hope this helps.
I have windows xp and when I plug in my headphones and then decide to unplug them I can not listen to my computer unless I reboot.
Advice please, Thanks