Folder with question mark fix!

Good afternoon

I followed all steps to fix the problem, found here in similar cases, but i wasnt able.

First, I tried the first aid, but no problems found.

Second, i tried to reinstall the os x but it couldn't find or show me the disk to select for the installation.

Last, i tried to erase the disk but the utility tool doesnt let me erase (the option is not available)

Any help will be appreciated.

Thank you!