problems with 3d printer

[theKingOfT.E.G.Harry]

i am having a problem with a prusa i3 clone using slic3r it prints well enough most of my proyects but i am trying to print a half circle beam and the printer wont even start heating i tried the same configs with at least 20 other parts and those work great, any ideas about why it wont take the program would be appreciated.

[Hackentosher]

Maybe the stl is bad? Try another slicer like Cura or Repetier Host. 

[theKingOfT.E.G.Harry]

its not the stl i sliced it with symplify and cura and it keeps happening th slicer does its job the gcode in preview look right but the machine wont select it