Studio 1557: No sound from internal speakers

My Studio 1557 has no sound from internal/in-built speakers.
Symptoms:
* Internal speakers emit no sound (Error code: 1B63:061B)
* Both headphone jacks emit sound
* No sound from sub-woofer (Error code: 1B63:111B)
* Internal Microphone Recording failed test. (Error code: 1B63:1D1B)
* Side Microphone Recording failed test. (Error code: 1B63:181B)
* Speaker Functionality Test failed. (Error code: 4C00:00619)
* Reinstalling audio driver does not help
History:
I slept listening to music from one of the headphone jacks through the headphone inlet that comes with Logitech PC speakers. The next evening I wanted to Skype and I could not hear any sounds from the internal speakers.
I uninstalled Skype, but no solution. I reinsatlled the IDT HD Sound drivers from the original CD by Dell and even updated it, but no solution. The sound is OK through the headphone jacks.

Please help!!

Thank you.
The headphone jack inlet can be seen here (the little black thing): http://www.amazon.com/Logitech-LS21...=2025&creative=165953&creativeASIN=B0015C30J0

 

Hi, I was able to determine the source of the problem and solved it.

I opened the PC and found the problem to have been due to unconnected internal speakers.

I had disassembled the PC some time ago to deal with an overheat problem (successfully); I then forgot to re-connect the speakers. I was thrown into a wild goose chase by Dell Diagnostics which reported that all connections were proper.


Anyway, thanks so much. And sorry to bother you due to my ineptitude.