There is no real cause for this issue, just windows being windows. For some reason windows starts creates a temporary profile for you and renames your original profile to .BAK.
How to Fix - Run Regedit
open the registry editor by typing regedit in command prompt, from the start menu or run menu. If you have trouble finding it the file is located in C:\Windows\regedit.exe
Once the window open navigate using the left pane to
HKEY_LOCAL_MACHINE -> Software -> Microsoft -> Windows NT - > Profile List
Here you will be presented with a list of profiles currently on your local machine, note that there will be a two profile with the same ID (letters and number) the only difference being that one will have a .BAK on the end of it.
If you highlight .BAK file you will notice that this is your original profile that has been renamed with a .bak which makes it unusable by windows and it will jump to the other profile without .BAK , which in this case will be a temporary profile.
The fix is simple - Remove .BAK from the correct profile and rename the temporary one to .BAK or .OLD. note: you may have to rename the temp profile to .old before you remove the .bak otherwise it will say that you have duplicate profile id's
log off and back on , and your all done