Hi Piyush,
Thank you for the post.
The default Administrator account is disabled if an account with administrator privileges exists.
Now let’s try the following method to logon the default Administrator account:
1. Put the Windows Vista installation disc in the disc drive, and then start the computer.
2. Press a key when the message indicating "Press any key to boot from CD or DVD …". appears.
3. Select a language, a time, a currency, and a keyboard or another input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type the following line and press Enter:
net user administrator /active:yes
Note: There is a space between “administrator” and “/active:yes”.
8. Restart the computer and logon the default Administrator account.
Can we logon it now?
Hope it helps.
Best regards,
Tim Quan
Microsoft Online Community Support