MacBook Pro sound issues

Hello everyone
I have a problem with my MacBook Pro's sound. It all worked great until today, now the internal speakers work perfectly and when I plug in my headphones, either nothing happens or the sound is greyed out. I've tried googling this, but Google only brought out similar problems when headphones work and internal speakers don't, with red light coming out of the port.There's no red light coming out of my headphone port...I checked my headphones and they work both with my iPod and my other computer, so that's probably the laptop's issue. Any way to fix this without Apple Store assistance?

Thank you in advance

First, try re-starting the machine.

The internal speakers still work/don't work when you plug in the headphones?

When you plug in the headphones, do they show up in Sound preferences or only the internal speakers?

Thank you for your reply
I've restarted it several times, it doesn't seem to fix anything.
No, the internal speakers don't work when the headphones are plugged in.
When I plug in the headphones, they show up as "digital out" in the Preferences, but if I try to adjust sound, it shows a write circle with a line crossed through it and it doesn't adjust anything.