Replying to Sony Movie Studio HD

I have an old mac that i have been editing my gopro footage on (imovie) and has been slow, but the video quality is very clear and overall good.  i also have a pc that i planned to do most of my editing on but since the Windows Movie Maker did not readily accept the gopro footage, i figured a convinient fix for the problem would be Sony Movie Studio HD 10, which i have used before and really like.  the problem came when i tried to edit some of the gopro footage.  the quality was awful in Sony Movie Studio. 

if i clicked on the file of the video, it would play as a quicktime video in great quality.  but as soon as i drag it into Movie Studio, it goes to complete shit.  in Movie Studio, the footage is recognizable, but barely.

what should i do to get better quality in the editing system? Huge thanks to anyone that can help