Hi, you can try to use command prompt to reset your lost password. I have used it to reset sql sa password successfully on sql server 2000/2005.
First, open a command prompt (Start -> Run -> cmd)
Then, type the follow commands, and press Enter after each line:
Osql –S yourservername –E
1> EXEC sp_password NULL, 'yourpassword', 'sa'
2> GO
It could help you. And I know a sql reset tool which can easily and instantly reset your sql sa password, you can try it also. http://www.passwordunlocker.com/sql-server-password-recovery.html