I have posted on this before but it is happening more and more and is being caused by a windows update. The first thing you can try is to reboot in SAFE MODE. When the computer is booting hit the F8 key and choose to start in SAFE MODE. After you have successfully logged in then you can restart and Windows should log in normally.
If not then try this registry fix:
To Fix the User Account Profile
If none of this works, make sure you don't have bad hardware and it is corrupting your profile and data. Test your hardware and if all is good then just create a new user and log into it and move all your data from your users file to the new profile. You will have to setup any email accounts you had in your existing profile but other than that everything else can be copied and pasted. Your main folders of concern will be MY DOCUMENTS, FAVORITES, DESKTOP. In XP it will be the same along with the MY PICTURES, MY MUSIC AND MY VIDEOS.
If all else fails call a computer repair person.
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