Many times, even with all other applications closed, computers store information in the form of temporary files or caches.
For example, You connect to a net-station, using WinAmp. The streaming audio will send packets to Your WinAmp player, which are buffered and pre-cached. Often, if You always keep Your "cookies" and temp files, even just the simple "My Documents" settings on a computer, which store recently accessed files in easily/quickly grabbed forms, or always keep Your "downloaded program files," then chances are whatever audio sound card device You used to listen (even just once) to that streaming audio or to a song You downloaded (even opening it up from a temp file) has been assigned to the WimAmp player. So, even when it's not open, Your computer has a "cookie" or temp file setting that tells it (in the computer's Registry) that WinAmp will use the sound card the next time You open WinAmp up and try to play something on it. This keeps the computer from constantly having to reset the listening settings on whatever player You use. Constant resetting of settings, over a long period of time, not only is annoying to wait for but it will eventually fragment Your hard drive.
Another example is if You downloaded a Zip file from somewhere.
That Zip file is stored in temporary memory on Your computer, even if You fully close the WinZip or WinRar opening device and even if You delete the Zipped folder(s) from Your drive. It sits in there until You clear Your "cookies" and temporary cache files.
If clearing the temp cache doesn't help, like the previous poster suggested, open up Your (on most Windows operating systems)
Start >Settings > Control Panel > Sounds and Multimedia folder and check out the hardware settings, to find what Your sound card is set for.
Also, in most music software, there are Tools or Options tabs that let You select which audio device is gonna be used for that session. Setting those options almost always sets up a preset in a dat or ini file in the music software's system folder which will tell the software to use those settings in the future, whenever You open up the program. Almost always, these options tabs let You select multiple pathways, multiple sound devices and to prioritize which applications use which devices in which order. For example, in my Cakewalk software I can set it up so that if I'm listening to a net-station with my WinAmp player and I suddenly get an idea to record something in Cakewalk, if I open up Cakewalk, it doesn't try to access the sound card (since WinAmp's using it right now) and instead looks for my MIDI "to host" plug, between my instrument amps/keyboards/microphones and my computer. This is because my instruments all have tone generators hooked up to them in some way, which serve as sound generators for MIDI settings in Cakewalk tracks. So, until I specifically turn off my WinAmp and turn on the Cakewalk's use of my sound card, like if I want to sample real audio mp3s or wav files onto audio tracks in Acid loops, until I tell it to use the sound card, Cakewalk just allows my other applications to have the sound card as their output device.
Acid loops and other programs (most of them) also have presets You can set up for Your "normal" template, which tells the software, "hey, every time you open up, I want you to give me 2 audio tracks and 2 MIDI tracks in the window. Not only that, but I want you to have both audio and MIDI tracks with the setting: 'INPUT DEVICE' - Direct to Host, 'OUTPUT DEVICE' - None."
This will make it so that every time You open up Acid loops software, it sets up 4 tracks for You, ready to use, and none of them are trying to access Your sound card. Then, when You're ready to use them, You can just switch the output device to being Your sound card.
There are a lot of other tricks like this.
It sounds like what's happening is when You open up a music program, it has presettings that tell the program it wants to use Your sound card for both Input and Output. (You probably imported audio data, if You're using Acid loops, and listened to it with Your sound card)
Also, sounds like when the program tries to do this, it detects some temporary file somewhere that tells it another application is waiting to use that same sound card. In other words, the other application is waiting in line to use the card, and it's at the front of the line, whereas the music software is somewhere in line behind the other application.
Hope You figure it out.
