Log back into Laptop

Hello,

Yesterday, my skype got updated and then my problem started. After i lock my screen, I have a continuous flashes of the log in screen and then the black screen. Nothing else works except shutting down my Sony Vaio laptop. This causes me to loose some of my work in the process. When i press the Ctrl + Alt + Del keys, it causes a pop up to come saying that if anything happens then press Esc or shut down with my power button. I don't know what to do, please help me.