X axis seems to ignore its endstop when printing.

I'm using RAMPS 1.4 with ultimachine's sprinter firmware for mechanical endstops and when I attempt to print with pronterface, my X axis goes home to its endstop, touches it, moves a few milimeters away, then back towards the endstop and keeps going. I can hear the motor straining when it does this so I usually switch off the power within a few seconds.

My endstops work perfectly when I manually move any axis in pronterface, does anyone have any idea what might be wrong? Any help is appreciated!

You say this only happens when you print. What happens when you press the Home button for the X Axis? If the home button operates normally, then the next place I would look at is the Gcode itself. Chances are though that the home button is going to exhibit the same behavior.

What happens when you try this:
enter the following GCode command with the carriage NOT in the home location: M119
this will print the end stop status
Next, trip the end stop with your finger and hold it in that position and enter the same command again.
What is the status reporting in each case?

My endstops change state when they're depressed and my x axis seems to home properly. Could it be something in my firmware?

The end stops are only used when homing. They establish the zero position. After zero is established, the firmware should prevent motion beyond the endstop. It might be possible through the use of improperly coded axis resets to fool the firmware into allowing unsafe moves. Could you post the first 50 or so lines of your G Code?

Sure thing, here it is.

; generated by Slic3r 0.9.8 on 2013-03-04 at 12:38:10

; layer_height = 0.4
; perimeters = 3
; top_solid_layers = 3
; bottom_solid_layers = 3
; fill_density = 0.4
; perimeter_speed = 30
; infill_speed = 60
; travel_speed = 130
; scale = 1
; nozzle_diameter = 0.5
; filament_diameter = 3.05
; extrusion_multiplier = 1
; perimeters extrusion width = 0.53mm
; infill extrusion width = 0.53mm
; first layer extrusion width = 1.00mm

M107
M190 S65 ; wait for bed temperature to be reached
M104 S190 ; set temperature
G28 ; home all axes
M109 S190 ; wait for temperature to be reached
G90 ; use absolute coordinates
G21 ; set units to millimeters
G92 E0
M82 ; use absolute distances for extrusion
G1 F1800.000 E-1.00000
G92 E0
G1 Z0.500 F7800.000
G1 X114.560 Y114.180
G1 F1800.000 E1.00000
G1 X113.980 Y114.740 F540.000 E1.04925
G1 X113.550 Y115.080 E1.08274
G1 X113.100 Y115.380 E1.11578
G1 X112.390 Y115.760 E1.16498
G1 X111.630 Y116.060 E1.21490
G1 X111.110 Y116.200 E1.24780
G1 X110.580 Y116.310 E1.28087
G1 X109.770 Y116.390 E1.33059
G1 X90.220 Y116.390 E2.52494
G1 X89.950 Y116.370 E2.54148
G1 X89.410 Y116.310 E2.57468
G1 X88.880 Y116.200 E2.60774
G1 X88.360 Y116.060 E2.64064
G1 X87.850 Y115.870 E2.67389
G1 X87.360 Y115.640 E2.70696
G1 X86.890 Y115.380 E2.73978
G1 X86.440 Y115.080 E2.77282
G1 X85.810 Y114.560 E2.82272

There doesn't seem to be anything wrong with the G code I was looking for some unusual axis resets, but you are only resetting the E axis - which is correct. I don't know what else to suggest.

Sounds like your slicer is not positioning print correctly or "home" is not in the correct spot relative to your slicing software.

Most of the time home is bottom or front left corner. (Print head in this position).

By default endstops only function during home, so after homing you can hit them and not get the machine to stop. SKipped steps will also render the software endstops usless.

Alright so I've changed the HOME_DIR variables under endstop settings in configuration.h from -1 to 1 for each axis.

When I attempted to print, my Y axis aligned itself to its center and my X axis tried to move outside of the build area. I immediately switched off the power and upon turning the power back on, the X axis moved about a cm to the left and began printing on the far right side of the build area.

I'm absolutely stumped. Anyone know where I can go from here?