Why the Looping?

OK so I am using an atmega 2560 with an Ethernet shield and reading an sd card off of it.
The issue I am having is if i add a timer interrupt to the setup the setup loops forever… what???

#include <SPI.h>
#include <SD.h>
#include <ctype.h>
File myFile;

struct parameters {
  int intValue;
  boolean booleanValue;
  String stringValue;
} settings;
// Setting for SD-card reader
const int chipSelect = 4;


void setup() {

  Serial.begin(9600);
  Serial.println("Starting...");
  pinMode(10, OUTPUT);
  digitalWrite(10,HIGH);
  if (!SD.begin(chipSelect)) {
    Serial.println("initialization failed!");
    return;
  }
  //getSettings();
  Serial.print("Interger Value: ");
  Serial.println(settings.intValue);
  Serial.print("Boolean Value: ");
  Serial.println(settings.booleanValue);
  Serial.print("String Value: ");
  Serial.println(settings.stringValue);
  timer4();
}

void timer4(){
  //Timer 4: Set to .1 second intervals
  TCCR4A = 0;
  TCCR4B = 0;
  TCNT4  = 0;
  OCR4A = 975.5625;
  TCCR4B |= (1 << WGM42);
  TCCR4B |= (1 << CS42) | (1 << CS40);
  TIMSK4 |= (1 << OCIE4A);
}

void loop() {
  //Currently nothing happining here.
}

OCR4A = 975.5625;

You cannot put floats into that field. It is a 16-bit unsigned integer.

TIMSK4 |= (1 << OCIE4A);

You have turned on the Timer/Counter Output Compare A Match interrupt but do not have an interrupt handler for it.