Its possible that your default sound device got changed. You will need to do some diving.
Did you check if you have any missing drivers?
Hit Windows Key+R and put devmgmt.msc into the run box and see if there are any missing drivers for any of your sound devices,
I'd also recommend checking your sound setting on your taskbar right-click on your speaker icon and click "Sound" when the new window pops up click on the Playback tab and see what devices you have, Before you do this next part plug your earphones back to where you normally have them. You can then go through the list of devices right-click on it and click "test" once you've found the one that has sound make sure that that device is set to Default (you will see that button on...