I have an M-audio fast track soundcard and it worked fine for a while. But now I can only hear FL Studio sounds when I am working but when I plaz a MP3 for example I don't hear any sounds. It shows me that there is no Soundcard Output but the input works fine. Any Idea what is going wrong? And why I can hear Fl Studios sounds but no other sounds from the PC?

Go into control panel stuff, under playback devices, choose the M-Audio card as default. I assume the stock onboard card is selected, so you only hear the M-Audio when it is specifically selected, such as in a daw.

I tried that already more times, disconnected and connected it but the card always shows up just in the input section and not in the playback section. Like if it wasn't connected, but than again, why does it work with the input sounds and why does it work with fl studio?

I don't know what is meant by "input" section, my control panel on Win7 has playback and recording, and I have my USB M-Audio card set as default, when I turn it off it goes back to onboard soundcard.

By Input I mean recording. In the recording section I can select the M-Audio card, but in the playback section it seems like there was no soundcard connected, I can just select the standard computer soundcard.

That's weird, I've used the fast track pro w/Xp, Vista, and Win7 and it shows up in control panel's playback as well as recording. It just seems odd.

I would email M-Audio.

Good idea, I'll do that. Btw I use the M-Audio Fast Track Ultra 8R. It worked fine up to now, don't know what I did but now it simply doesn't work anymore.

Have you tried rebooting the pc after having turned it off for some seconds?
Have you tried to detect new hardware?
Have you tried reinstalling the drivers?

Did it happen after a blue screen? Did it happen after you turned the computer off without unloading the os?

M-Audio Fast Track Pro has a driver bug that has been described many times in the M-Audio forum but never fixed.

In your Sound and Audio Controls, specify the original soundcard as the default. You can still use the FTP in your DAW (FL Studio) but all other players will go through your soundcard.

http://forums.m-audio.com/showthread.php?3-USB-Audio-Series- FAQ-s-Answers-to-commonly-asked-questions

I fised the problem with the missing Device. I just did a right mouseclick when I was in the Playback section and there I selected "show deactivated devices" or something like that and selected the soundcard than as standard device. Now MP3s work but if I want to listen to Youtube or Soundcloud for example I can't hear any sound. And in the output section it even doesn't show that there is a sound being played. Very strange all that.