Fcp x issue -- please help!

hi there,

I'm having an issue w/ fcpx and i was wondering if you could help me.

i'll have a file split into separate video and audio tracks in the timeline so the audio track is above or below the video track, then a couple minutes later ill go back, and the audio track is sitting on top of the video track, and if i play that part, the screen is black instead of the correct video and audio that should play.

do you know what could be causing this? it's driving me crazy!

thanks,

myles