LCD Works on USB not on Power Source

Hey gize, so when i turn on the power source the LCD lights up but it does not show any control or option, is a blank light. But when i connect on the USB port of the PC, the Menu appears and starts working normally.
What might be the problem?

Thanks

From [reprap.org]

Known issues and limitations

1. Overheating 5V regulator on the Arduino Mega

Unless you provide external 5V power or provide 5V through USB cable, the regulator on the Arduino supplies 5V power to the Arduino, the RAMPS (which uses very little) and anything else connected to it. With nothing else powered from the RAMPS, the voltage regulator will run quite warm but not overheat (in tests, I was even able to turn up the input voltage from 12V to 15V without overheating it). With a 20x4 LCD connected, it's still OK with 12V input. However, if you power a servo or a graphic LCD from the RAMPS, then you will almost certainly overheat the voltage regulator. The usual symptom is that the system will not work unless it is connected to a PC via USB. Or the system may work for a few minutes, hours or days, then fail.

Thanks for the reply!

The thing is that i use an external power source and the only thing connected to the 5V port on the Ramps is the power source itself and the extruder fan. What else might be the problem? I have just changed the flat cables to new ones, but problem persists also, so i am starting to think its not a cable problem too. OH and my LCD is the one from 2004.

OBS: I just took the 5v out of the ramps and powered on to test it and the LCD didnt even turned on, i have put it back the wires and then came back to turning on ( only the light, no menu or options).

Edited 1 time(s). Last edit at 09/21/2017 11:21PM by hapo1313.

What 5v port? there is no 5v port on the ramps there is a 12v 5amp and a 12v 11amp

And the mega shouldnt have any power to the dc jack either, unless you have removed D1 from the ramps. Then then it needs 7-12v

Edited 1 time(s). Last edit at 09/21/2017 11:50PM by Dust.

Ohh yeah, i have made a mistake, i was talking about the 5A port lol. But where should i check the power of the LCD then? It is only connected by the adapted and flat cables.

OBS: It used to work before fine, once i have reassigned the ramps/mega into a full closure i has stopped working

Edited 1 time(s). Last edit at 09/22/2017 12:37AM by hapo1313.