problem in debugging timers with interrupt

hi,i have written a program for timer 0 using interrupt. when i am debugging my code using keil uvision4 simulator,it doesn't come in the Interrupt service routine.i have made change in startup.s file but still it doen't come in ISR.
here is my source code
/*#include<LPC214x.h>
void toisr(void) __irq;
int main()
{ PINSEL0=0x00000000; IODIR0=0x000000ff; T0PR=0x00007503; T0TCR=0x00000002; T0MCR=0x00000003; T0MR0=1000; T0TCR=0x00000001; VICVectAddr1=(unsigned)toisr; VICVectCntl1=0x00000011; VICIntEnable=0x00000010; while(1);
}

void toisr(void) __irq
{ IOSET0=0x000000ff; T0IR=0x00000001; VICVectAddr1=0x00000000;
} */
and here are the changes that i have made in vector address of startup.s file
/*
; Exception Vectors
; Mapped to Address 0.
; Absolute addressing mode must be used.
; Dummy Handlers are implemented as infinite loops which can be modified.

IMPORT toisr

Vectors LDR PC, Reset_Addr LDR PC, Undef_Addr LDR PC, SWI_Addr LDR PC, PAbt_Addr LDR PC, DAbt_Addr NOP ; Reserved Vector
; LDR PC, IRQ_Addr LDR PC, [PC, #-0x0FF0] ; Vector from VicVectAddr LDR PC, FIQ_Addr

Reset_Addr DCD Reset_Handler
Undef_Addr DCD Undef_Handler
SWI_Addr DCD SWI_Handler
PAbt_Addr DCD PAbt_Handler
DAbt_Addr DCD DAbt_Handler DCD 0 ; Reserved Address
IRQ_Addr DCD toisr
FIQ_Addr DCD FIQ_Handler

Undef_Handler B Undef_Handler
SWI_Handler B SWI_Handler
PAbt_Handler B PAbt_Handler
DAbt_Handler B DAbt_Handler
;IRQ_Handler B toisr
FIQ_Handler B FIQ_Handler

; Reset Handler

EXPORT Reset_Handler
Reset_Handler
*/
help me to find out the problem.