DDJ-400 No sound through headphones.

Using DDJ400 with Windows 10 PC for four months with no issues. Now I can't get any sound through headphones, either from master or channel cue.

Headphone controls are greyed out in Mixer panel...

I am using default audio settings.....

I'm using Rekordbox 5.4.3.

Cue buttons pressed and headphone volume turned up.

I've checked headphones are working fine.

I've tried using all three USB ports of my PC.

No obvious debris in headphone port.

HELP PLEASE!