Electronic – UART Program is Stuck when Enable Interrupt with PIC24F

I'm using PIC24FJ64GB002.
I want to use it for UART by RS232C with my PC.

The problem is that, if I make "IEC0bits.U1TXIE = 1;", the program doesn't work at all.
I mean even LED does not become bright.
However, even if "IEC0bits.U1TXIE = 0", "IEC0bits.U1RXIE = 1" or "IEC0bits.U1RXIE = 0;", the program works except for the matter of the baud rate.

I want to know what is wrong and how to make it right.
But, I guess it can be due to the hardware problem.

And, excuse me for my English as I'm not a native speaker.

My environment;
OS: Windows 7,
IDE: MPLABX,
Compiler: XC16

/* 
 * File:   main_pic24fSerial.c
 * Author: Raven Iqqe
 *
 * Created on 2013/09/26, 18:56
 */

#include <stdio.h>
#include <stdlib.h>
#include <xc.h>
#include <uart.h>

#define OUTSTR  "Hello!\0"
#define ALPHA   'A'
#define GRNLED  LATBbits.LATB15
#define YLWLED  LATBbits.LATB14
#define REDLED  LATBbits.LATB13

// CONFIG4
#pragma config DSWDTPS = DSWDTPSF       // DSWDT Postscale Select (1:2,147,483,648 (25.7 days))
#pragma config DSWDTOSC = LPRC          // Deep Sleep Watchdog Timer Oscillator Select (DSWDT uses Low Power RC Oscillator (LPRC))
#pragma config RTCOSC = SOSC            // RTCC Reference Oscillator  Select (RTCC uses Secondary Oscillator (SOSC))
#pragma config DSBOREN = ON             // Deep Sleep BOR Enable bit (BOR enabled in Deep Sleep)
#pragma config DSWDTEN = ON             // Deep Sleep Watchdog Timer (DSWDT enabled)

// CONFIG3
#pragma config WPFP = WPFP63            // Write Protection Flash Page Segment Boundary (Highest Page (same as page 42))
#pragma config SOSCSEL = SOSC           // Secondary Oscillator Pin Mode Select (SOSC pins in Default (high drive-strength) Oscillator Mode)
#pragma config WUTSEL = LEG             // Voltage Regulator Wake-up Time Select (Default regulator start-up time used)
#pragma config WPDIS = WPDIS            // Segment Write Protection Disable (Segmented code protection disabled)
#pragma config WPCFG = WPCFGDIS         // Write Protect Configuration Page Select (Last page and Flash Configuration words are unprotected)
#pragma config WPEND = WPENDMEM         // Segment Write Protection End Page Select (Write Protect from WPFP to the last page of memory)

// CONFIG2
#pragma config POSCMOD = XT             // Primary Oscillator Select (Primary Oscillator Enabled, XT)
#pragma config I2C1SEL = PRI            // I2C1 Pin Select bit (Use default SCL1/SDA1 pins for I2C1 )
#pragma config IOL1WAY = ON             // IOLOCK One-Way Set Enable (Once set, the IOLOCK bit cannot be cleared)
#pragma config OSCIOFNC = OFF           // OSCO Pin Configuration (OSCO pin functions as clock output (CLKO))
#pragma config FCKSM = CSECME           // Clock Switching and Fail-Safe Clock Monitor (Sw Enabled, Mon Enabled)
#pragma config FNOSC = FRCDIV           // Initial Oscillator Select (Fast RC Oscillator with Postscaler (FRCDIV))
#pragma config PLL96MHZ = ON            // 96MHz PLL Startup Select (96 MHz PLL Startup is enabled automatically on start-up)
#pragma config PLLDIV = NODIV           // USB 96 MHz PLL Prescaler Select (Oscillator input divided by 12 (48 MHz input))
#pragma config IESO = ON                // Internal External Switchover (IESO mode (Two-Speed Start-up) enabled)

// CONFIG1
#pragma config WDTPS = PS32768          // Watchdog Timer Postscaler (1:32,768)
#pragma config FWPSA = PR128            // WDT Prescaler (Prescaler ratio of 1:128)
#pragma config WINDIS = OFF             // Windowed WDT (Standard Watchdog Timer enabled,(Windowed-mode is disabled))
#pragma config FWDTEN = ON              // Watchdog Timer (Watchdog Timer is enabled)
#pragma config ICS = PGx1               // Emulator Pin Placement Select bits (Emulator functions are shared with PGEC1/PGED1)
#pragma config GWRP = OFF               // General Segment Write Protect (Writes to program memory are allowed)
#pragma config GCP = OFF                // General Segment Code Protect (Code protection is disabled)
#pragma config JTAGEN = ON              // JTAG Port Enable (JTAG port is enabled)

// Local Variables Declaration
char str[32] = OUTSTR;

// Prototype Declaration
char outputstr(char *);
void delay(void);

// Main Function
int main(void) {///*
    // Oscillator Setting
    OSCCONbits.COSC = 0b001;    // Current oscillator is FRC with PLL.
    OSCCONbits.NOSC = 0b010;    // New oscillator is 8MHz.

    OSCCONbits.CLKLOCK = 0;
    OSCCONbits.IOLOCK = 0;
    OSCCONbits.LOCK = 0;
    OSCCONbits.CF = 0;
    OSCCONbits.POSCEN = 0;
    OSCCONbits.SOSCEN = 0;
    OSCCONbits.OSWEN = 1;

    // Clock Division Setting
    CLKDIVbits.ROI = 0;         // No division of clock
    CLKDIVbits.DOZE = 0b000;
    CLKDIVbits.DOZEN = 0;
    CLKDIVbits.RCDIV = 0b000;
    CLKDIVbits.CPDIV = 0b00;
    CLKDIVbits.PLLEN = 0;

    // Port Setting
    TRISBbits.TRISB10 = 1;
    TRISBbits.TRISB11 = 1;
    TRISBbits.TRISB13 = 0;  // Red LED
    TRISBbits.TRISB14 = 0;  // Yellow LED
    TRISBbits.TRISB15 = 0;  // Green LED
    LATB = 0;

    // UART Pin Setting
    RPINR18bits.U1RXR = 11;
    RPOR5bits.RP10R = 3;

    // AD Converter Setting
    AD1PCFG = 0xFFFF;       // Disable all A/D convertion.

    // Interrupt Setting
    SRbits.IPL = 0b111;     // CPU Interrupt Priority
    INTCON1bits.NSTDIS = 0; // Interrupt nesting is enabled.

    // UART Setting
    U1MODEbits.UARTEN = 1;
    U1MODEbits.UEN = 0b11;
    U1MODEbits.USIDL = 0;
    U1MODEbits.ABAUD = 0;
    U1MODEbits.BRGH = 0;
    U1MODEbits.PDSEL = 0b00;
    U1MODEbits.STSEL = 0;

    U1STAbits.UTXISEL0 = 0;
    U1STAbits.UTXISEL1 = 0;
    U1STAbits.UTXEN = 1;
    U1STAbits.UTXINV = 0;
    U1STAbits.URXISEL = 0b00;

    U1BRG = 207;

    IPC3bits.U1TXIP = 0b001;
    IPC2bits.U1RXIP = 0b001;
    IFS0bits.U1TXIF = 0;
    IFS0bits.U1RXIF = 0;
    IEC0bits.U1TXIE = 1;        // Here!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    IEC0bits.U1RXIE = 1;


    // Main Routine
    while(1){
        if(OSCCONbits.CF == 1){
            REDLED = 1;
        }

        GRNLED = 1;
        outputstr(str);

        delay();
    }

    return (EXIT_SUCCESS);
}

// Normal Functions ************************************************************

// String Output
char outputstr(char *string){
    while(*string){                 // Output string until \0 (null).
        while (!IFS0bits.U1TXIF);   // Wait for completion of output
        U1TXREG = *string++;        // Output string and increment string's address.
    }
    YLWLED = 1;

    return(1);
}

void delay(void){
    int i, n;
    for(n=0; n<32; n++){
        for(i=0; i<10000; i++);
    }
}