UART Program is Stuck when Enable Interrupt with PIC24F

[vivitern]

I'm using PIC24FJ64GB002 (datasheet: http://www.kynix.com/uploadfiles/pdf8798/PIC24FJ64GB002-I2fSO_94644.pdf ).

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++);
}
}