Very strange problem with audio waveform (15.4.1)

Hi guys,

I recently installed Premiere Pro (15.4.1 build 6) on my new pc and I have this strange problem, never seen before and didn't find any solutions in the forum.

The problem is that I can't see the audio waveform properly, in the souce panel:

The contrast is inexistest and I can't see the waveform very well.

What is the problem?

Thanks to all.