The modem will draw about 2amps momentarily when in use. That is more than six times the maximum capacity of the power supply in your photo. Even with the capacitor on the shield acting as a reservoir you are trying to draw way more than it will supply.
Load your code into the IDE. Press Ctrl+T (or find auto format in the menu). Then copy the code and paste it to the forum in code tags. There is a sticky about how to use the forum at the top of the page.