I’ve got my PC set up to go to sleep after a period of time if no activity. I am using windows 7. Can I change my settings so that if winamp or some other audio program is playing the PC knows not to go to sleep?
Edit to add: I’m using the HDMI port to connect the PC to my TV so I can use the TV’s sound system. I don’t think I have this problem when I use the headphone jack.
Try this:
Open Control Panel -> Power Options. Click on ‘Change plan settings’ for whichever power plan is currently in use. In the next window, click on 'Change advanced power settings. A new window will open; scroll down in the list until you get to ‘Multimedia settings->When sharing media’, and make sure you’re set to ‘Prevent idling to sleep’. In the same section, set the ‘When playing video’ settings to ‘Optimize video quality’.
Of course, if your computer already has these settings active, this won’t help 
If that doesn’t work, your best bet is either to get an audio player program that has a “don’t sleep feature,” design a script that will detect activity of the all your audio applications, or just disable sleep when you listen to music and reenable it when you are done.
BTW, Windows Media Player has such an option, although they call it “allow screensaver” or some such.
This plugin may work for Winamp. It’s only for preventing screen turn off, but the method used for that may also prevent sleep.
Also, I’ve read that you have to actually use the balanced profile to make sure that Windows 7 will listen to applications about not sleeping. You can still tweak the profile to make it identical to any other profile, so it’s not that big a deal unless you actually need a third power plan.