problems recording with microphone

I have been using Audacity like this: Opened a karaoke mp3 file in and then recorded singing on other tracks using an ordinary headset with mic. At first it worked alright but now it starts “clipping” the singing everytime no matter which recording level I use unless I sing at first along to an external karaoke track and then import the same mp3 file to audacity afterwards. Can anyone explain that? I use Windows 7 and have an 8192 MB ram acer computer.

I presume that what you are doing is “importing” the karaoke MP3 as one track in Audacity and then recording your voice to a new track?

If you click the “Solo” button on the recorded track, do you hear just the singing or do you also hear the backing track?

Yes normally I would insert the track and then make a new track for singing afterwards. I can turn on solo and then I only here the solo track, tracks.

I can’t explain the symptoms, but I’m not completely clear what the symptoms are, however these are two areas that I suggest you look:
Windows Sound Enhancements should be off:
Check the recording level in the Windows Sounds Control Panel: