Help login

Hello,
Hello, IMac-21.5??
This reboot is not working! Help!! It's just making that noise that it makes until I've put in the correct password...I was trying to change the name on the login screen. It asked me for the I'd n password again. I kept the same password n changed the name...so I thought. I turned computer off and back on and the name is the same, but the same password does not work and it just beeps at me when I try the control s. I can't do anything nut look at the login screen...a brand new computer gone to waste?! I will cry.