Dell xps 8300 thx trustudio pc with altec-lansing speakers

Connected Altec-Lansing ACS54 computer speaker system with subwoofer to my new Dell XPS 8300 desktop, but there is no audio. Doesn't look like the hardware is recognized. The Dell-installed sound system is the THX TruStudio PC option. Any ideas re the source of the problem? Thanks

Sorry for late post
I too have the same setup
Dell XPS 8300
i7... HD6770
Altec lansing ATP3

try connecting either to the back or to the front and see
If u have a pair of headphones then
Connect altec to the back and headphones to the front
in that case only the headphones will work
so go to realtek audio mgr
then click on the folder icon in analog box
select disable front panel jack detection
If you have dell speakers too the u can try inserting its green jack in the front panel and altec behind
Now try again
If it still doesnt resolve issues
try to reinstall THX and realtek audio mgr drivers and software
(before reinstalling uninstall them first)
connect all jacks properly and reboot.
and see if problem is gone.

^_^ matter of fact - do check in volume box u havent muted it anyway