Z motor not moving during auto home My Monoprice maker select recently fried its melzi board.  So I went out and purchased a ramps 1.4 kit.  I've wired it all up and Flash the firmware with marlin(most recent build).  When it boots up it boots up fine I go to prepare.  And then I go to move axis I can move the X Y and Z axis and the access is moving in the correct direction.  I go to auto home and the X and Y axis home properly but the z-axis does not move at all.  Even though I can move it manually.    Does anyone have any suggestions.  I checked the end stop for the z-axis even though I know it probably has nothing to do with it and it has continuity when the end stop switch is depressed.
Alright, I have figured everything out with the help of #reprap IRC community.

Issue #1 - Z axis not moving during zero.  Just as tjb1 suggested the issue was that it thought it was hitting the endstop, I needed to invert the logic of the endstop within the configuration.h

const bool Z_MAX_ENDSTOP_INVERTING = true;


Issue #2 - No Heated bed controls.  The issue resided with the configuration of the heated bed within the configuration.h.  The bed was not defined correctly(I do not have the solution for this one as I found a pre-configured configuration.h for the Monoprice maker Select and  after loading the firmware it worked

Issue #3 - The extruder motor would not move.  This was the biggest issue and came down to it being a cheap RAMPS/Arduino.  E0's pinouts were not working properly so I took off the driver and wiring from E0 and put it on E1 then altered the pins_RAMPS.h and swapped the values for E1 and E0 pinouts.  after reloading the firmware the extruder then moved fine.

#define E0_STEP_PIN        36
#define E0_DIR_PIN         34
#define E0_ENABLE_PIN      30

#define E1_STEP_PIN        26
#define E1_DIR_PIN         28
#define E1_ENABLE_PIN      24