We're sorry to hear about this. Let us know the version of Premiere Pro that you are using & the type of media file you are working with (format/codec, frame rate & frame size). Also, are you getting any error messages while importing the media?
Although you do not tell us what type of file you are trying to import, I could assume that it is too heavy for your mac or that it has been recorded with a cell phone, which usually generates some problems since they use a variable frame rate (especially mid-range cell phones low) and that generates the problem
Hope you can solve
Let us know