Perhaps due to the latency of your soundcard there is a shift between the music you listen and the voice you records? In this case you can drag the voice on the track to synchronise it with the music.
u have to enable bit matched recording in the settings of the nike on the cpu, i hope u have a decent pc cause if u dont ur finished with magix i have an i7 processor and 6gb ddr3 , if ur serious u have to invest and yes its a dell studio 435, u can buy a good cpu 4 cheap now adays
better yet, turn off masteren disable effects in the mixer, and effects over masteren, also go to file program settings, click audio, midi and make sure its on wave driver, also when u use the keyboard sellect asio 4 all, when u mix n record use wave driver, i hate dragging it back seems like its never on time