Kind of impossible to tell really for that information.

All the obvious things;

Broken cable,

Correct cable,

Has Windows changed the port assignment of your serial port? (Can easily
happen if you are using a USB serial adapter)

Can you open the port in a terminal emulator such as TeraTerm or
HyperTerminal? (if not then it is a PC issue rather than a target
issue).

Check Windows Device Manager to check that the port is available and
what its assignment is.

Clifford

Clifford Slocombe wrote:
> Kind of impossible to tell really for that information.
>
> All the obvious things;
>
> Broken cable,
>
> Correct cable,
>
> Has Windows changed the port assignment of your serial port? (Can easily
> happen if you are using a USB serial adapter)
>
> Can you open the port in a terminal emulator such as TeraTerm or
> HyperTerminal? (if not then it is a PC issue rather than a target
> issue).
>
> Check Windows Device Manager to check that the port is available and
> what its assignment is.
>
> Clifford

Thanks Clifford Slocombe..
i just tested my board with Hyper Terminal,it seems like no respond from
the board although it is connected..and i also tried to use serial to
USB converter and connect the board to pc through USB port but still
cannot communicate with the board..is it any way to test whether my
board is still working or not?
hope to hear from u soon..thanks..

Just some ideas:

(1) double check if you have the Pin P0.14 low during power-on or reset.
The bootloader will not start when the Pin is high and a valid
user-application is in flash. So tools like lpc21isp, the Philips ISP
tool or flash-magic can not connect (see for example
http://www.olimex.com/dev/images/lpc-h2129-sch.gif Jumper BSL).

(2) Check if the power-supply to the LPC (both 3,3 and 1,8V) and
RS232-transceiver is available (DMM) and stable(scope).

(3) Check if the XTAL is connected and oscillating with a scope.

(3) double check your RS232-transceiver circuit and do a
"loop-back"-test. This could be done like this:
- make sure the bootloader does not get started (P0.14 high) to keep
the LPC's bootloader for configuring the UART TX as output and driving
it.
 OR 
- if you have the option to disconnect the LPC from the
RS232-transceiver (MAX3232 or whatever is used on your board) with
jumpers or "solder-jumpers" disconnect at least the LPC TX-line from the
transceiver
- Now that the LPC does not drive TX you can connect the two pins of the
RS232-transceiver on the logic-side (those connected to RX/TX of the
LPC) and test if characters you send with Hypterterm are send back and
shown in the Hyperterm Windows (I suggest to use the Bray Terminal for
such experiments)

If the test fails there might be a broken cable, wrong cable (maybe a
RX/TX crossed), broken connector or broken transceiver-IC.

(4) check if the LPC RX/TX Pins and the LPC itself are still working:
Since you can not access the bootloader to upload firmware to the LPC
flash you need an option to flash though JTAG (hopefully you have not
set the "magic protection value"). If you do not have any
hardware/software for this you can build a Wiggler and use OpenOCD or
H-JTAG with it. Than create a small application which configures the
TX-pin as GPIO output, the RX-pin as GPIO input and then reads the state
of the RX-Pin and sets the TX-Pin depending on the RX state in a loop.
Use Hyperterm/Bray-Terminal to send characters to the device. They
should be "echoed" back.

Hope this helps
Martin Thomas