Waitaminit ... when you reset it, it should go into bootloader?
So when you bought an LPC2138 for your target board, how did the bootloader get programmed into it?
Did you buy it specifically from the same vendor as the development board, as an LPC2138 with the correct bootloader pre-programmed?
Or did you buy an un-programmed device and program in the bootloader yourself?
EDIT : the bootloader appears to be pre-programmed at manufacture.
However the only way to clear security keys on these chips is a full chip erase, and it is unclear to me what that does to the original bootloader...
So here's one scenario : the bootloader is not being started after reset.
I found a dev board manual with some troubleshooting information on starting the bootloader - at reset. P0.14 must see logic level 0 to neter the bootloader.
Another possible scenario : a genuine, hopefully working, but re-used part after a full-chip erase.
So some of the following may still be useful - it ought to be possible to read the flash memory via JTAG and verify whether the bootloader is present and correct...
Here's an outline : you need programming hardware. The dev board may be able to do that : is there anything in its doc about "programming target devices"?
Otherwise, programming hardware can be as simple as an "ISP interface" usually a 6-pin JTAG connector on your board. This connects to a JTAG adapter (probably your dev board) by ribbon cable, and communicates (usually via USB) with programming software on your development computer.
Finding, installing and using it is up to you...
Add a link to your development board for more detailed help.