When you type your password and press Enter, you will typically see the error message “The User Profile Service failed the logon” and “The user profile cannot be loaded”, and you’ll be returned to the logon screen.
WARNING: Some people have lost files by using Method 1 below, so create a backup of your hard disk, or just files you cannot afford to lose before trying anything which involves editing the Windows Registry. There are various programs which will allow you to make a copy of your entire disk, but you will need a second disk with sufficient capacity, and may even need a second PC or laptop in order to copy the disk (if you can't...