Where's my user account?

I was installing some software on my desktop in the office just now. After finished installing, it required me to restart my computer. So I restarted my pc and then try to login with my username and password.

Guess what? I couldn't login.. typo? let me try again? canot again? let me type slowly, make sure caps were not on and still cannot? What the hell? Let's see what the message says.. no such user? what? I've been using this user login for almost 3 yrs now and out of a sudden it says no such user on this domain? arggg...

I got my colleague to help me fix this. According to him, my user account suddenly disappeared! I didn't know the user account will go missing just like that.. ~sigh .. what a day.. when you are busy, all sorts of funny thing will happened..