I am not able to solve the problem properly, but still its working now.
What i do is as follow:-
I thought i had used programmer/debugger and thats why the bootloader which is residing in the ARM's memory gets removed, and this might be a very bad situation for me, because i can't program my board as my programmer is not working and bootloader has been erased.
This is what i thought, but this is not the case, i tried serial interface and LPC210x Software to program my board and it works.
Now a question arises in my mind?? ARM Controllers has bootloader code when they are manufactured, am i right, means NXP has provided the bootloader code in its memory by default and we cant erase it??
Okay then i again started to use my parallel port programmer and it works this time, i debug also and it works.
I did it 3-4 times and then stop H-JTAG Server and then re-started it, again same problem occurs it doesn't recognize my controller.
Then again i use bootloader software and program board and then try the Parallel port programmer and yes it again works.
I dont know the logic behind this, its really very weird thing if someone knows why this happen then please explain me.