The icons of a cloud file or folder missing can be due to two things
The OneDrive Agent is not running
Please start OneDrive from Start Menu or restart your computer. To confirm, check the icons next to the clock in the bottom right corner. You should have a blue cloud icon. Remember, the icon might be hidden. To reveal, click the up arrow next to the icons you see.
The library is no longer synched to your computer
To add the library, please follow this article