Have you tried creating a new account and check if the problem occurs there as well?
I've seen a post on TechNet where they suggest it as a possible solution.
An accepted solution there was Startup Repair:
If the issue persists, you can also
perform Startup Repair. Since you are
now logging on in Windows Vista
Operating System, you need to use
Windows Vista installation disc. To do
this, please take the following steps.
Note: Please ensure that the DVD-ROM
is the first booting device.
- Please insert the Windows Vista DVD and reboot the computer.
- When we are prompted to press a key to boot from the DVD, please press
Enter or the space bar.
- Choose your language settings, and then click Next.
- Click Repair your computer.
- Select the operating system you want to repair, and then click Next.
- On the System Recovery Options menu, click Startup Repair. Startup
Repair might prompt you to make
choices as it tries to fix the
problem, and if necessary, it might
restart your computer as it makes
Another suggestion they made there makes you lave the trouble making files behind (note this was under XP I think):
You need to create another profile for
each user, with all the same
attributes and privilidges for that
user, then go into an admin account
(not the account that your changing or
the account that your setting up, a
different one) then in folder options
make sure that "show hidden files and
folders" is checked, and "hide
protected operating system files" is
unchecked. then go to the
Settings\Old_Username folder" Press
and hold down the CTRL key while you
click each file and subfolder in this
folder, EXCEPT the following files:
Ntuser.ini. right click and choose
copy, go to the C:\Documents and
Settings\New_Username folder and right
click and choose paste. reboot the
computer and then you should be able
to log on as the new user