Personal OneDrive suddenly stopped working

I recommend opening https://onedrive.live.com in an InPrivate browser window to confirm whether the problem persists independently of your browser session. Additionally, visit https://account.microsoft.com/storage to check your storage allowance and https://account.microsoft.com/services to verify your subscription status.Accounts exceeding their storage limits for an extended period may become frozen. You can review Microsoft's official explanation here: https://support.microsoft.com/onedrive/what-does-it-mean-when-your-onedrive-account-is-frozen

Could you confirm whether you can still access other Microsoft services, such as Outlook.com, whether your account has exceeded its storage quota recently, and whether the problem occurs on another device or network? These details will help determine whether the issue is isolated to OneDrive.

You can try accessing OneDrive web instead of OneDrive client if that works. Additionally you can try OnDrive web version in Private / InCognito mode or in a different browser. If that works then its the client that might have the issue, you can either reset or reinstall the client.