13" Macbook Air auto restarts at login screen

Hey guys, having an issue here that just came up suddenly.

After shutting down my macbook, and turning it on, everything went as per normal and the login screen came up. I keyed in my password, and then the loading bar comes up, but after loading around 1/8 of it, my macbook just auto restarts (like the apple sound comes up again), and then I'm brought back into the login screen, but then this time, my background wallpaper went back to default. I tried using the touchpad and the sensitivity of the cursor is not what I adjusted it to be.

I am using OS X Yosemite, Version 10.10.3.

Was wondering if anyone faced a problem like this and have a solution? Thanks!