Turned on for the 1st time since 4 years...No data?

I turned on my MacBook Pro for the first time since about 4 years. Instead of going to the account screen, the Mac showed a choose-your-language screen and then the OS X Utility. It seems that there is no data on the hard drive (except for ~300MB in Other) according to Disk Utility.

I restarted the Mac with the Startup Option by pressing the option key and the only available disk is called “Recovery-10.11.4”.

Is the data actually gone? Is it possible to recover the data and /or account? Thank you for your help!