Hi!

I recently bought the 777, and I was astonished! 

Fantastic aircraft and everything but just one thing.. 

The sounds worked perfectly for the first 5-6 days I think but suddenly, it disappeared one day.. Any ideas on what I could do?

I had the same issue. Go into your fmc, options and then sound. go to device and make sure that device is the same as your default device in windows ie headset, speakers etc. hope this helps. if you need a visual you can go into the the pmdg introduction and go to page 106.