Audacity doesn´t capture PC' sounds

Audacity doesnt capture sounds fron PC. I got Windows XP Pro. I formated my PC , but now Audacity ( neither do others) (sic) cant detect sounds from my PC.
I configured the preferences this way:
-Server MME. I’ve Changed to Windows DirectSound but doesn’t work.
Playback Device : RealTeh HD Audio Output.
Record Device: RealTeh HD Audio iput : Mezcla Estereo (Mix Stereo)
Chanels: Stereos.
From Microphone it record. Either mix stereo or from microphone.
Look like the PC doesn’t generate sounds.
Would you like to help me, please.
Excuse me my English.

You should be able to record from Stereo Mix and capture Sounds Playing on the Computer.