A Microsoft file hosting and synchronization service.
Do you mean the OneDrive cloud icon is no longer showing near the clock on your Windows taskbar, or did you unlink/sign out of OneDrive?
If so, click Start, type OneDrive, and open the OneDrive app. If prompted, sign in with the Microsoft account you use for OneDrive. This should start OneDrive again and restore the cloud icon near the clock.
If OneDrive opens but asks you to set it up again, let me know what message you see.
Click "Add comment" to let me know.
Thanks!