Rx then Pin 13 Flashing ????

I got a project (Arduino uno connected to ESP8266 and some other Hardware).

In general it works but I got some Problems with Blynk loosing connection because Buffer overflow that happens sometimes frequently, sometimes not once for over an hour (it's not related to flooding the server).

I now thought it might be related to the serial monitor, so I closed it.

But as soon as I close the serial Monitor my Arduino stops working entirely.

On my Arduino the RX LED is flashing, afterwards 2 or 3 times the Pin 13 LED. this repeads until I start the serial monitor again. Then it does work as before.

What does this mean?

If only we could see your code so we knew exactly what you were doing and even maybe try it for ourselves .....

Gorkde: But as soon as I close the serial Monitor my Arduino stops working entirely.

On my Arduino the RX LED is flashing, afterwards 2 or 3 times the Pin 13 LED. this repeads until I start the serial monitor again. Then it does work as before.

What does this mean?

Are you aware that opening or closing the serial monitor will reset the Arduino?

No I didnt but even after I did close the monitor and reset the Arduino it continues flashing.

Once I power it with battery instead the USB cable I used for programming it works as normal.

but for some reason once its connected to the USB its just working with serial monitor on.

You're using 1.6.8 of the IDE on windows aren't you? That has a bug that causes it to continually reset all connected Arduinos when the IDE is open and serial monitor is not open.

Use 1.6.5r5 or 1.6.9.