The DuetWifi generates 3.3V on board from 5V, supplied by USB, external 5v or from the VIN supply though another convertor. If you have no 3.3V light with USB plugged in with a board that was previously working the first point is to try it without endstops and other inputs connected and then can short 3.3V to ground if they have an issue
As I said, I tried it to the point without anything connected. The endstops were the first stops as this was one of the solutions that I found on the internet but it's not working. The board worked fine and when the print was over and everything cooled down, I turned the printer off and went to re-connect it to the new wifi. Now I can't do anything.