Why does the screen keeps turning on/off after connecting to MBP13?

Hello, I have a question concerning the Apple Cinema Display 24" connected to Macbook Pro 13" (2010) with Mountain Lion installed on it. The screen keeps turning on and off constantly, so does the screen of the MBP. Both show the blue screen (normal while connecting any external display) than the desktop appears on ACD screen and a second later it goes back to blue and so on. While connected both screens flicker with blue screen, desktop, blue screen, desktop until disconnected. The built-in USB hub and charging work normally. Does anybody know what may cause the issue? Is it hardware or software? Thanks in advance for any help!