|The ATX mboard on is always powered in some places, even when the computer is not running, as long as the main battery is connected and not completely discharged, and/or the AC adapter is connected and powering the laptop.|
Did you have both the main battery and the AC adapter disconnected at all times when you were fiddling with unplugging / plugging in things inside the case, or plugging in or unplugging the ram?
NOTE that most if not all more recent laptops will NOT run on the AC adapter alone. The main battery has to be installed too, and be charged to at least a minimal capacity as well.
If the battery is not charged to at least a minimal capacity when it is by itself, or when the AC adapter is also connected, the computer will not start up, until the AC adapter has charged it to at least a minimal capacity.
How old is the main battery? People tend to neglect changing that. Typically they are able to be charged to their rated capacity for a year, then they begin to deteriorate (none of them have longer than a 1 year warranty, according to what I've encountered). By two years they typically can't be charged to anywhere near their rated capacity, and the older they get, the worse that situation gets. They often develop internal shorts when they are older - if so, when you attempt to charge them they get HOT rather than just warm, and they have been known to get hot enough to cause a fire. If they are internally shorted, when you measure it's voltage it may never get to it's full rated value.
Laptop no video on the LCD display, and battery / AC adapter / charging T - shooting.
See response 1:
In addtion to the possiblity the wiring to the LCD display is damaged, it could be shorting, which may fry the video adapter, or the mboard, or whatever.
The backlight is a CCFL - cold cathode flourescent lamp - I would think the voltage inverter supplies AC high voltage to it, just like for other flourescent lamps. Were you measuring AC or DC voltage? If the computer is not working properly otherwise, or if the baclight is failing which is quite common, no voltage from it may not be significant.
Similar to the power switch almost always not being the problem, there's probably nothing wrong with the lid switch, but you could try bypassing it (shorting across it) after opening up the case. Just don't fiddle with anything while power is connected to the laptop. In any case, the lid switch has no effect on the VGA port video output if there's nothing else wrong.
Does this laptop have a separate power module? If so, you haven't mentioned that - it could be damaged, although that seems to be very rare, unless you damaged it.