Windows 7 suddenly rejecting correct password at login.

I recently set a password for my computer. I locked my computer and typed it in (so I know for a fact that its right). But when I started my PC this morning it automatically brings me to a screen saying 'User name and password is incorrect'. I press OK and re-enter my password (WHICH IS 100% CORRECT) it says it's wrong.

So when my computer is starting up I pressed F8 and went into System repair. It brings me to a screen to enter a password, I type the EXACT same password as before and it lets me in. I am trying to log into my user account 'Tyquan' when my PC starts up AND on the system repair.

I only have one account which is administrator, I never set a password when configuring my windows for the first time, and even if I did it would be one of 3 passwords (I tried them all and all stupid variations of them that they could be)

I'm just confused as to why my computer is rejecting my password in one screen but accepting it in another.

Im running windows 7 64-bit

Thanks in advance for any of your help