You can use Winternals software to reset your system admin password, also you can use some linux based utilties to reset the password
- Stellar Phoenix Password Recovery – Simple startup utility resets a forgotten admin or users’ password using a familiar Windows-like program interface instead of command-line.
- Password Kit – Top rated version of Passware’s Password recovery app, supports Windows Vista and RAID/SCSI/SATA drives.
- Petter Nordahl-Hagen’s Offline NT Password & Registry Editor – A great boot CD/Floppy that can reset the local administrator’s password.
- Openwall’s John the Ripper – Good boot floppy with cracking capabilities.
- EBCD – Emergency Boot CD – Bootable CD, intended for system recovery in the case of software or hardware faults.
Also check this article from petril on password recovery.