No sound from speakers

SOURCE: sound is working but internal speaker is not working

Connecting headphones to the system will disabled the internal speakers until the headphone jack is disconnected, at which such time the internal speakers should function again.

If you disconnect the headphones and the internal speakers are not re-activated, then there may be damaged to the microswitch in the jack. (Try rebooting after the headphones are disconnected too)

SOURCE: Dell latitude D620, no speaker sound

you will have to uninstall your audio device, and uninstall SKYPE and re install the audio device and don't re install SKYPE, you can do this by going to add or remove programs, and remove SKYPE first and unplug u r headset and mic, and after removing skype you can reboot the computer, and sometimes the conflict is resolved, otherwise then go into your device manager in system manager and find audio devices, unistall the driver or Update the driver, and reinstall it and the reboot, that should take care of the problem.

SOURCE: Audio from laptop speakers is fine, headphones are not.

Do these headphones work OK in another machine??

If not they are faulty / If so then sound port may be faulty.
'Ensure it is enabled in BIOS. press DEL key when booting and look for similar.

SOURCE: When external speakers are plugged into my laptop

Suggestion: do a system restore back to last week when they worked.

SOURCE: I have a Latitude D600

I dont think the JACK is the problem, I suspect a bad headphone wire (intermittent) or an incorrect driver, headphone jacks in laptops are software controlled, (no mechanical switch inside) if you hear sound in both the headphones and the speakes it is a driver issue, try updating the driver, if the headphone wire is erratic it can fool the software that controlls the input and do crazy things also...

Good luck!