Help!

Guys i have no idea what just happened...

I was running my macbook pro off battery and it died. I plugged it back in, and unlike my previous powerbook G4, i had to push the on/off button to turn it on, to recover it from its 'battery dead stand-by mode'. the system rebooted like i had just turned it on.

when it boots, i notice that the dock is different and the wallpaper has changed. i thought, thats strange. then i notice EVERYTHING has been deleted. it was like i just installed the OS.

my applications i had installed eg azureus, firefox, office, etc were all there still in the current applications folder...but when i open a finder window, on the left, there is no music, pictures, user folders...

I have lost all my settings, files, basically everything... why has this done this and what do i do?

Thanks

This might be too simple a reason, but you or the computer somehow may have created a new user's account and the thing is booting into it. If so, it would be created with all the system's default settings.

Check the Users folder to see if more than your usual log-in account is in it. And/or log off and log in, to see if a list of user choices is available.