Videos and sound keep lagging + double speed

Hi

I just installed the test version of Premiere Pro 2017 to help me make a decision for a video editing program.

I have the problem that imported clips stutter heavily when starting the playback. This problem happens in the media preview window but also

for clips in the timeline, even after I rendered the sequence. The sound also sounds horribly distorted. It looks like the video would jump back a few frames periodically.

Additionally, all clips run with about double the speed they should. It doesn't depend on the used material, i tested GoPro footage with different settings but also the Windows example video (wildlife).

What i did:

- Create a new project

- Add a new sequnce with the AVCHD 1080p-60fps setting

- Import the footages (mainly GoPro 1080p, 60fps clips)

My System:

i7 2700k @4GHz

16GB RAM

nvidia GTX780

Windows 7 64 Bit

Has anybody any ideas what the problem could be? I would greatly appreciate any tips that could help me to solve this.

Thanks.