When trying to access the Windows Store, you get this error:
You can’t access the Windows Store because you’re signed in to this PC using a temporary or guest account. Please sign in using a different account.
Assuming that you’re not logged in as a guest, this happens because Windows 8 has given you a temporary acount even though you have a full account. This can happen if your Windows profile is corrupt or unreadable (perhaps due to permissions being set incorrectly on one of the folders in your profile). To fix this, fix the temporary profile issue (recreate the profile, etc).