A Microsoft file hosting and synchronization service.
Is this when you are trying on the browser, or in the app?
If the browser, try clearing the cache and cookies or try using a different browser.
If the app on your computer, try resetting it:
Press the Windows key + R
Copy and paste this text into the Run window and press Enter:
%localappdata%\Microsoft\OneDrive\onedrive.exe /reset
That will reset OneDrive
After a couple of minutes, the OneDrive cloud icon should show in the system tray.
If it doesn’t start, open Start, find OneDrive and start it.