There are two methods that you can try.
One would be to create a new Microsoft account for your computer and login with that.
Another, that would let you keep all of your settings and your existing Microsoft account, would be to do a "Computer Refresh". This will copy all of your files and settings and all of your "Modern Desktop Windows" programs, and
then reinstalls Widows 8 and the Modern Desktop Windows" programs that you installed from the Windows 8 Store. Then it will copy back your files. It will not reinstall any Desktop programs that you previously installed.
If you were using Windows Live Mail, make sure to backup your mail storage folder first, in case Windows does not copy it. I have not test it to see if it does or not. It does do a good job of copying all of your files, so I would not be surprised if it
did copy this as well, but better to play it safe than sorry with things.
To do a Windows Refresh, you will need to be logged in with a local admin user profile, and not with a Standard user profile.
You can click on the Modern Desktop and type: refresh
Make sure to select 'reinstall Windows and save/copy all files'