First, boot into Safe mode: Start your PC, and press
If you’re using Vista or windows 7, you can remove the administrator password with ubuntu linux. Careful! This gets complicated. download the current ubuntu version from find.pcworld.com/71065. double-click the just-downloaded .iso file. Windows may start a program that burns your ubuntu CD. If it doesn’t, download and install ISO recorder (find.pcworld.com/60657), and then try again. Boot off the CD. when asked, click the Try Ubuntu button. Install the software: From the menus in the top-right corner of the screen, select Check the two options not yet checked: and Click then after the program is done processing, select from the menus in the top-right corner.
In the resulting window’s Search field, enter chntpw. a program with that name should appear in the subsequent list of packages. Click it and select. Click the toolbar icon. Click and wait until the installation is complete. Now mount your drive: From the top menus, select then your internal hard drive or windows partition. When it’s mounted, a File browser window (much like windows explorer) will appear. double-click the folder icons to go to the windows drive’s windows\System32\config folder. Leave this window up. From the top menus, select arrange the two windows so that you can see the top section of the File browser window behind the Terminal window.
In the Terminal command-line window, type cd /media/ (note the space after ) and the path to your config folder, using the folder names at the top as a guide. (note: ubuntu’s Terminal is case-sensitive.) Then press
Source of Information : PC World Magazine February 2011