I haven't use the Macbook pro for a little while. It runs using the power adapter for the battery is dead. I recently tried to log in but could not. On another partition is Windows. I have no problems booting into Windows. Pretty sure of the password for the Mac. The screen doesn't shimmer then come up blank telling me that it was wrong, instead I get the spinning wheel of death and after 5min. its still the same thing, can't do anything but turn off the computer.

What to do?
Could this happen because of a dead battery, that I'm unable to get logged in?