sound track turned gray

I have worked on a track for almost 3 days and I always saved it on my external hard drive. When I opened it today, the sound track (previously blue) turned all grey and I can`t play it. Well, when I hit play it looks like it is playing but there is no sound. I really need to recover the track!

Thank you for your answers.
Audacity (2.1.0)

Have you deleted, moved or renamed any folders on your hard drive? It looks like the project _data folder is missing.
Were there any errors or warnings when you opened the project?