I have a Gateway 400vtx laptop with Windows XP and my sound is no longer working. I have tried system restore, checked the volume, tried speakers and headphones, uninstalled and reinstalled my sound card (Sigma Tel-C Audio), tried updating the sound driver (there was no more recent driver) and gone entirely through both the Windows and Gateway sound troubleshooters. Nothing has helped and my computer shows all sound hardware and software as being functional. Please help! How can I fix this?