|if you have 2 Windows CD you can do a repair of the existing installtion.|
Visit this link, It has detailed info about the repair install.It will not erase any data of your.
In the process of repairing , when you are on below screen
Press Ctrl + F10
It will bring up the command prompt..Now type this command exactly.
net user admin1 /add
net localgroup admin1 /add
net user admin1 abc@123
After executing below 3 commands let the setup finish..
after reboot You should see the users you created, If any issues with the old user you can try the admin1 we just created. the password is abc@123