I've just had this problem on my computer, and I just fixed it.
It seems to be caused by a horrendous bug in Vista that renames your User
Account Profile as a backup, and then creates a new user account with the
same name but with nothing in it.
I googled it and followed several bits of advice but none of them worked,
but I managed to fix it with a combination of ideas.
This is how I did it:
1. Boot up in Safe Mode. To do this, hit the F8 key while the computer is
booting, and then scroll down to the "Safe Mode" option and press enter. On
my computer the user account icon appeared, but bigger than normal, and I
clicked it and it loaded my desktop in safe mode. It came up with an error
bubble saying that my user account hadn't loaded properly, but i just ignored
this.
2. Click the Start Button and in the white "Start Search" space at the
bottom type "regedit" (without the quotation marks). This will open the
registry editor.
3. In the left-hand pane, navigate by clicking the little triangles next to
the following folders:
HKEY_LOCAL_MACHINE
SOFTWARE
Microsoft
Windows NT
CurrentVersion
ProfileList
You should now have a list of folders all starting with S-1-5- and then a
number.
(You might need to drag the divider between the 2 panes of the window across
so you can read the whole folder name)
Look at the end of each name and you should see one with .bak at the end of
it, and there will be another one above it with exactly the same name but
without .bak at the end.
The one that's got .bak at the end is your old User Profile that Vista has
now made into a backup, and the one without .bak after it is the new empty
User Profile that Vista has created.
Just to check that this is the case, have a look in the right-hand pane for
each of the 2 folders and look at what's written after "ProfileImagePath".
For the folder with .bak at the end it should say C:\Users\ and then your
usual User Account name, and for the one that doesn't have .bak at the end it
should say C:\Users\TEMP.
What you need to do now is to rename the folders in the left-hand pane so
that the one with .bak at the end changes back to being the one containing
your proper User Profile and the new one without .bak at the end becomes the
backup. Do do this follow the next step:
4. Right click on the folder with .bak at the end and then click "rename",
and just change the ".bak" part to ".bk" - i.e. just remove the "a" from the
middle - (this is just to allow you to change the other one to have .bak at
the end). Press enter or click on some blank part of the screen for the
change to take effect.
Then, right click the one that doesn't have .bak at the end and click
"rename". Remove the .bak from the end and press enter or click anywhere on
some blank part of the screen to accept the change.
Then, right click on the one that now has .bk at the end, choose "rename"
and add the "a" back into the middle, so it now has .bak at the end. Press
enter or click on blank park of screen to accept the change.
Close the regedit window.
5. Click the Start Button and then "Restart". It should work now. Fingers
crossed.
