Which model of GoPro? The later versions seem to use High Efficiency Video Coding (HEVC), also known as H.265 by default which Premier Elements cannot work with on a Windows PC (& and as I understand it only the later PE version can on a MAC).
There are numerous threads on exactly this subject hence , although I don't use a GoPro, I come up with these alternative workarounds:
1) For future videos change the setting on your GoPro to use the H,264 Codec.
2) For existing clips download & install the Handbrake tool and convert your H.265 clips to H..264.
The resulting file size will be much larger but the quality is retained as I understand it.