If your computer is off then OneDrive won't sync and your files won't upload or download.
The Onedrive client sync occurs when your computer is started, if Onedrive client is opened (it should appears a white cloud close to Windows time in systray bar) all your pending files should be sync to the cloud, by other hand if you left your computer without any activity and the Energy saving is off, probably the Internet connection will turn off and the syncing process it will stop.
So, I suggest you to check out the Energy saving settings:
https://support.microsoft.com/en-us/windows/how...
Made the changes correctly in order to avoid that the Internet connection or the hard-drive stop working.
Depending on what files are stored on OneDrive, some save automatically live like Excel, Word etc.
If Windows detects changes to files and folders, those too can get sync straight away.
The OneDrive sync app uses Windows Push Notification Services (WNS) to sync files in real time.
Any metadata changes happen immediately, like renaming or deleting files.
Downloading content also starts a specific session with the client.
Using Microsoft OneDrive, you can keep personal files stored on your computer in sync with the cloud.
Those same files are then synced automatically and available on other devices.
Doing this is an easy way to ensure your desktop and laptop always have access to the same set of documents, photos, and more.
If you've signed in to Windows with a Microsoft account, you don't even need to log in to OneDrive—it does that automatically.
However, syncing OneDrive with other clouds like Google Drive and Dropbox has more procedures.