Here are two pages that turned up for me. Both from Google, and having not used Vista, I can't vouch for either of them.
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If you changed the only administrator account to a standard user account,
you should be able to go to Safe Mode and use the built-in administrator
account.
Reboot the computer and when it first starts to boot, start tapping the F8
Key. You will eventually see a black screen with a menu. Use the Arrow Keys
to select Safe Mode and press Enter. It will take a few minutes to start
safe mode. When the login screen appears, you should see an account named
Administrator, there should not be a password associated with this account,
just select the account and press the Enter Key to log on.
Go into Control Panel / User Accounts. Select the Manage Another Account
option, on the next screen, select the Standard account that you want to
change. Click the "Change the account type" option. On the next screen,
select the Administrator account type and click the Change Account TYpe
Button.
Close everything and reboot the computer. You should now be able to logon
with your old administrator account.
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Well, there is a way out of this situation, but it is very complex, and
requires you to have the Windows installation DVD.
(For pictures, please view these instructions on my website):
http://www.jimmah.com/vista/Administ..._of_admin.aspx
1 Click on the start orb. Write down your username (the name listed
right below your picture on the start menu).
2 Place your Windows Installation DVD into your DVD drive
3 Restart your computer
4 When prompted, press a key on your keyboard to boot from the DVD
5 Select your language options and click Next (See picture)
6 Select the option at the bottom to repair your computer (See picture)
7 Select your Windows installation from the list. Make sure you notate
what drive letter it is installed on.
8 Select the last option from the list to open a Command Prompt (See
picture)
9 Type the following command, and press enter:
regedit
10 On the left, click on HKEY_LOCAL_MACHINE
11 Click the File menu at the top, and then click Load Hive
12 Open "computer"
13 Double-click on the drive that Windows is installed on (you wrote
this drive letter down in step 7)
14 Double-click on the folder called Windows
15 Double-click on the folder called System32
16 Double-click on the folder called Config
17 Click on the file called SAM and click Open
18 Type "Target SAM" into the box and click OK
19 Expand the HKEY_LOCAL_MACHINE folder by clicking on the triangle next
to it
20 Expand the Target SAM folder by clicking on the triangle next to it
21 Expand the SAM folder by clicking on the triangle next to it
22 Expand the Domains folder by clicking on the triangle next to it
23 Expand the Accounts folder by clicking on the triangle next to it
24 Expand the Users folder by clicking on the triangle next to it
25 Click on the folder named 000001F4
26 Double-click the item in the right called "F"
You are now presented with an editor. You will see two columns: a list
of letters and numbers grouped in pairs on the left, with a list of
symbols on the right. We will only be using the list of letters and
numbers on the left.
27 Find the spot in the left column that says "11".
28 Click to the immediate right of the 11, so that the flashing
insertion line is to the immediate right of 11
29 Press backspace to make the 11 disappear
30 Using the keyboard, type the number 10
This should change the information in the left column from
02,00,01,00,00,00,00,00,80,8c,d7,b2,e9,97,c7,01,00 ,00,00,00,00,00,00,
00,1f,ea,fd,ad,e9,97,c7,01,00,00,00,00,00,00,00,00 ,de,ad,60,9b,e9,97,
c7,01,f4,01,00,00,01,02,00,00,11, ...
TO:
02,00,01,00,00,00,00,00,80,8c,d7,b2,e9,97,c7,01,00 ,00,00,00,00,00,00,
00,1f,ea,fd,ad,e9,97,c7,01,00,00,00,00,00,00,00,00 ,de,ad,60,9b,e9,97,
c7,01,f4,01,00,00,01,02,00,00,10, ...
31 Click OK
32 Close regedit
33 Close the command prompt window and click on the 'Restart' button on
the window that gives you the list of options.
34 When your computer restarts, log in with the account named
'Administrator'. Use this emergency Administrator account to fix your
normal administrator account by using the user accounts control panel.
--
-JB
Microsoft MVP - Windows Shell/User
Windows Vista Support FAQ -
http://www.jimmah.com/vista/