Why are my earphones not working in my laptop

i have plugged in my headphone into my computer and normally i have a little menu kind of bar asking me whether i would like the sound coming out of the computer's mic or my earphones and i always click my earphones. When i go on to you tube i am able to hear any music i want on my earphones and no one else can hear it. It is fine. However when i was trying to plug in my earphones today nothing came up so i checked the sound and i could hear the sound without putting my earphones in. I do not know what to do.