Starting with Windows 8, your Microsoft Account carries a lot of data that Windows uses to personalize and make switching between devices easier. Things such as your wallpaper, accent color, saved passwords, bookmarks and a whole lot more are saved to the Microsoft cloud for syncing between devices whenever you sign into a new Windows PC.
This functionality is still apart of Windows even today with Windows 10, and up until recently users could go and delete that data from the cloud if they wished to do so. The webpage that allowed users to delete sync data from the cloud has been down for several days now, causing problems for many users looking to clear sync data from their Microsoft Account.
This tool was most handy when wanting to reset your Microsoft Account back to defaults, if you didn't want Windows to continue syncing old bookmarks, passwords and wallpapers. I used this tool very often when clean installing Windows, as it meant I could login to my new Windows 10 install without having my Microsoft Account sync a load of data that I didn't want it to.
You can attempt to access the tool at this link. We asked Microsoft what's going on with the tool, and if it would be back. Here's what they said:
Some users may be experiencing issues loading the webpage, and we are looking into it.
So in short, Microsoft hasn't yet told us why the webpage is down, and it's not clear when it'll be back online. We're hoping it'll be back sooner rather than later, as I'm sure many users are gearing up to clean install the Windows 10 Creators Update and would like to be able to start afresh with their Microsoft Account at the same time by deleting sync data from the cloud. We'll update this post once we know more.