why does video darken after I convert in Main concept??

I have been converting my big 14 gig video transfers into 2.5 gig files in MainConcept by converting them to DVD. In darker parts of the video I can't see anything. It's just pitch black with the sound. Am I converting it to the wrong thing because there are other choices such as mpeg 2, vcd and so on.. Thanks in advance for the help...