It could be that you have some liquid that made its way into your mod and is on your board. Maybe you can try and open it up to check and dry it out if there is any liquid in there. Or there might be a wire loose on the inside.
Mine got a wurm in die kop and refused to switch on.
What I did was to hold down the fire button and plug in the usb cable on the pc.
It then went into DFU in FS mode and once I removed the cable, started up properly.
No issues at the mo.
After playing around some more, I discovered charging wasnt working and after switching off, it doesnt switch on anymore.