Ethernet shield not receiving and trasnmitting when connect to pc

Here i'm testing connection between Ethernet Shield and PC(Local Server) attached on UNO. Everything works as expected receiving and transmitting data between local server and arduino. But this only working when i'm connect using USB cable. Problem arise when i'm try to self-powered Arduino Uno using batteries GP 12v 1.2Ah convert to 5v using DC to DC converter 1.5 to 35v.

Local server only hosted simple web page that control Arduino's pin.

Here is the workflow:

Arduino -> send data to -> local server = Work as expected Arduino -> received data from -> local server = Work as expected local server -> send data to -> Arduino = Work as expected local server -> received data from -> Arduino = Work as expected

What am i missing?

So are you trying to power it through the DC jack? Or are you still powering through USB, but with an external regulator? It's not clear.