Optiplex MT 3050, The PC does not switch on if I install a VGA card

Dear all!

The problem:  

Dell Optiplex MT 3050
The PC does not switch on if I install a VGA card. Vga card type: Gigabyte GV-N1030SL-2GL

This is a low power Geforce 1030, passive low profile card. It has no extra power connector. Theoretically, it consumes 30W under full load.

If I install the VGA card and give power to PC the fans run for 1 second and turn off. The PC does not switch on after this, the fans don't spin up.

If I remove the VGA card, the PC starts and operates normally. I've already tried with 2 different graphics card (of the same type).

Additional info: The PSU is 240W, it should run the system without any problems, the PC is brand new, I've just opened the factory sealed box an hour ago. 

Thank you for any assistance. 

Best, 

Gergo