VERY STRANGE PROBLEM with my 3D printer

Hi everybody,
I built a few months ago my 3D printer like the RepRap but with the print area larger. I mounted a motherboard Minitronics v1.0 (whit Marlin_v1) and the rest of the components are RepRap. I use the softwere Repetier-Host with Slic3r or Cura.
Everything works great, but takes out the unsolvable problem:
If I want to print something, the printer makes me the first 3-4 layers righteous, but then it goes crazy and begins to make a print path different from that of the g-code. For example, if I need to print a simple cylinder, it forms in the first 3 layers of perfect circles, but to the layer n. 4 extruder begins to break out of the circle and begins to make a linear path, after which resumed the circular path, but not on the layer n. 3, it print "in the air".
Please, if anyone has a solution, help me!

Maybe one of your motor drivers is overheating at that point.
Hence moving in one direction rather than in circles.
When you start again its cooled down.
When i first set mine up i used a cheap infra red thermometer to check the temp of the drivers heatsink.
Try adjusting the power or put a fan on the drivers, a desk fan would prove it.

Gordon

Thank you very much, I put a fan on the motherboard and the problem has been solved! THANK YOU!!

Excelent after all the knowledge and help ive got from the reprap project ive been able to give back and help someone.

You may need to still tune your motor drivers even if the fan stops them overheating.
They may not be working as efficiently as they can.
Loads of guides online on how to do it.

Gordon