My Dell Inspiron 15 will not boot up. Started randomly shutting down over a week period. Would also display a plaid screen which would require a hard shut down by me. I was trying to run Dell diagnostics on it and noted that the video card failed, but it could not complete the diagnostic without shutting down. Now the power supply light blinks on and off in a 10 second interval. It acts like it has no power, but I know the battery was charged. Help?