Manually resetting Windows account password

To reset account passwords in Windows without an existing administrator account privileges, there are two choices:

1) Do a repair install of Windows from your installation media, and after the initial reboot and “Installing Windows” screen, wait for Installing Devices and then hit Shift-F10 , then type in nusrmgr.cpl and hit enter to access the User Accounts in the Control Panel.

e.g.:
http://pubs.logicalexpressions.com/pub0009/lpmarticle.asp?id=305

Or

2) Use a third party password reset utility to create a password reset bootable disk, such as: http://pogostick.net/~pnh/ntpasswd/

The advantage to route #2 is that it is usually faster, however you generally are left best resetting passwords rather than creating a new one. You can then change from a blank password to an actual password once you have restored access to Windows.