Which Arduino are you using?
#include <SD.h>
512+ bytes per open file of you SRAM just went away.
String setH;
String setMinutes;
String setSeconds;
String minHour;
String minMinute;
String maxHour;
String maxMinute;
You are pissing away resources needlessly. You don't have enough to be wasting on the String class.
long brain_data[sampleSize];
Nearly 1/4 of the memory on a 328-based Arduino...
Serial.print("Initializing SD card..."); //so this is where the error occurs. This does not print out.
String literals end up in SRAM, unless you take some simple steps:
Serial.print(F("Initializing SD card...")); //so this is where the error occurs. This does not print out.
The problem is that you don't have near as much memory as you think you do.