Lights for ON and L dim and fade out when I connect 3.3V to rails

Hi, I've been working on my project for a while now and today the board just stopped responding. The Project is relatively simple, it involves the creation of sin waves and getting the output through the DAC pins. Until today it worked great however all of a sudden it stopped working. I rebuilt the circuit numerous times but everytime I connect the 3.3V pin to the rail as I have done before the green light on the board for ON dims andso does the orange one for L. A minute or so later both die.

I sam at the end of my ropes and have been trying to fix this mess for 3 hrs and am on the verge of breaking the board out of frustration. What is my possible issue and how can I fix it.

My project is due next thursday.

Connect 3.3V to what rail? The Due needs 5V power to drive its built-in DC-DC converter. There is a limit to how much current you can take from the 3.3V pin.

Says about powering the board .

5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

All I have done is connected the board to the computer via the USB cable and connected the 3.3V, first GND and A0 to a potentiometer. I had it in a similar config for a while now and never had this issue.

What could be the problem?