A product key is a 25-character code that's used to activate Windows and helps verify that Windows hasn't been used on more PCs than the Microsoft Software License Terms allow.

Learn how to check for, download, and install KB 2919355, an update for Windows 8.1 and Windows RT 8.1.

Learn how to find the serial number on your Surface so you can register your product or request service.

Resolve Windows blue screen errors with tips and resources to do your own troubleshooting, or contact the Microsoft support if you need more help.

If you have a Surface or Xbox, you can use your Microsoft account to check its warranty and make warranty claims.

Device encryption helps protect your data and it's available on a wide range of Windows devices.

Create list views to organize, sort, and filter data in different and specific ways; change the metadata, such as adding and deleting columns, and modifying validation rules; and use lists consistently across sites with content types, site columns, and templates.

Learn how to get the latest Windows updates to keep your device running smoothly and securely.

To review app, game or subscription purchases, track orders or view and print invoices, sign in to the order history page on your Microsoft account dashboard.

Find and remove a circular reference. You can also learn about the circular reference warning message and iterative calculation in Excel.