Sorry for the troubles. Which Melodyne edition and version is this? Do you use the standalone program or the plug-in? If it is the plug-in, which DAW are you using to host Melodyne? Which OS?
Also, how much RAM have you got? What kind of files are you trying to edit, i.e. full length tracks vs. short snippets, polyphonic vs. monophonic?
Can you find us a crash log? See also this thread