I have read your problem and you've stated that when you keep the reset button pressed the messages are readable, But when you depress the switch the display is blanked.

I think that it's possible that your program is maybe crashing , because you then would have the same result which would be undefined startup from the CPU.
Due to noise on the busses it could be possible that the diapay blanks.

Maybe you can implement a reset counter and than increment it when the processor starts up .
The value must always be the same unless you apply a manual reset
(This is something i use when searching for errors in Siemens Hicom PABX'S)
you can tell by the increment that the processor reset itself without human interference.

You can try to send a message in the startup routine and then see of this message is readable again.

If it is , you can asume that there is nothing wrong with your lCD module.

I have a hitachi 2*16 module which is attached directly to the cpu bus and i have used no buffers , the panel contains all the circuitry needed.

I can not immagine that short cable are causing this kind of mallfunction, because the input of the controller is data-latched (There has to be a clock pulse to write the new (blank) data into the device.)

i hope that this can help you solve your problem.

best regards.