- What OS did it come with?
- Do the speakers still work if you go back to those factory settings?
Just to exclude a hardware problem. If the headphone jack still works, a hardware issue would be my first guess, even if you and Dell think it's the OS or the driver.
I recently installed Windows 7 Ultimate on my Dell M1330 and my audio doesnt work (though my headphone jack works).
I have looked at several other forums for solutions for this problem,
installed several drivers (including but not limited to, R147073,
R167846, R171786, and what ever driver dell support recommended me
install) and I had my speakers and motherboard replaced.
I am pretty sure its a windows 7 problem (according to Dell tech support and my research).