I forgot my local PC administrator password is there a way to reset it without reinstall my whole OS.
You can try this http://sourceforge.net/project/showfiles.php?group_id=133599 - Ophcrack is a Windows password cracker based on a time-memory trade-off using rainbow tables. This is a new variant of Hellman's original trade-off, with better performance. It recovers 99.9% of alphanumeric passwords in seconds.
Download and save the ophcrack-livecd file. This is an ISO file that is used to create a bootable CD. If you have NERO available on the machine double clicking on the file will automatically invoke NERO. Nero will expand the ISO file and create a bootable CD. The bootable CD is a LINUX system that automatically invokes OPHCRACK when it is booted. It will find all users on the machine and list the passwords associated with them. I have used this program to determine the passwords for accounts on WinXP and Win2K systems. I have not tried it on VISTA but you can read all the gory details about the OPHCRACK project on the Source Forge web site.
If you are still need to reset your admin password private message me with your email address and I will email you a floppy disk imagine. It is very simple to use if you are having problems with the bootable os.