Can't log into Mac: Correct password denied after stand-by status in Macbook Pro

Hi everyone,

I am using a 2011 October purchased Macbook Pro 13'. The experience has been smooth with only minor problems until last night when I was getting back to use it after some stand-by time/ maybe it was only screen lock.

When normally typing in password under user name would grant you the usage, it suddenly rejected my correct password! I have tried a thousand times, checked Capital lock, keyboard typing, still denied. So I wondered if logging in using another user might help: wrong. I got stuck in creating the user and password, so I had to turn it off by pressing power off. I hoped it would work after I restart it; still didn't. The weird part is that it does not even show me my original user name any more: it shows me an apple logo, two columns where I can type in user name and password: on the left side of user name column there is a tiny arrow pointing to the left. However, no matter what (including using my only account that existed); it only shows the waiting/loading circle spinning. This takes forever and I end up staring at this for half a day and still nothing. When I clicked on the arrow, the page flips to left, appearing a totally blank screen with no columns but only option to sleep/restart/shut down.

After all these did not work put, I tried to go to Option - disk recovery, disk repair - after a short repair it says that the disk is okay/normal. But it still does not work.

Finally I have made some research and tried another thing: to go to the terminal to change user password: change saved but when I type into the blank columns my old user name and new password- not working.

Background info on my mac: have installed windows boot camp partition (not in use any more and planned to remove it and restore the space to MBP. and my mac partition is recently almost out of space/application room, if this could be the problem.

Would really appreciate an answer soon as i am a student who is highly dependent on laptop. And my current country does not have a apple store....