Printer randomly stops, Is the power supply bad?
It could be several things.

Your ramps board is overheating or has to much load on it. If you're not cooling the ramps board adding a fan may help the issue. 

I know Robo3D had this issue and started shipping with a fan to cool the ramps board.

The ramps/arduino board could be faulty, the firmware may have gotten corrupted or the current version has a bug in the code.

If you are not printing from the sdcard on the lcd controller and using software through a usb connection, that computer may be causing the issue as well.