Do you have another available admin accounts? If so, just Start computer by pressing F8 key to enter Advanced Boot Options before Windows 7 loading screen appears.
Choose Safe Mode at the Advanced Boot Options screen and Enter to login with the accessible admin account
Click Start and input lusrmgr.msc into the Search box. And you can reset the password.
if necessary, it is better for you to take a Windows password recovery tool to your password recovery, like Windows Password Unlocker, which allows you to reset the forgotten vista password with a bootble CD/DVD/USB flash drive. Just have a try.