how can I fix my del latitude d600 laptop it wont start up ?

Look here:
http://www.bay-wolf.com/portpostcodes.htm

Middle flashing and outside lit = RAM problem.

I don't see middle flashing and outside off.

REMOVE the battery and DISCONNECT the charger.

Try reseating your RAM moduls: Remove and replace each modul, one by one.
Try replacing your RAM if reseating don't work.

Electro
August 2013