DBG LED blinking

I am using Arduino MEGA for my 3d printer(self-built). During mid-print, the DBG-LED (Blue Light) keeps blinking and the print job stops. The arduino board was not responding. What does it mean when the light blinks? Is this a hardware problem?

Let me get this - you're asking a question about a self-built printer, with no mention of what software you're using?

The Arduino MEGA 2560 doesn't have a "DBG-LED". Are you using a RAMPS shield? If so, what revision?