please help, powerbook freeze electrical problem

hello
i have a nice pbook g4 1.6 ghz with a good behavior

from some time now the battery stop working properly, when i wasn´t connected to AC the computer after some minutes the computer just powers off with no previews warnings, therefore i use the computer connected to AC most of the time,
the other day i remove the keyboard to fix a key following the ifixit.com instructions i put everything together again, and later a terrible problem appears
the computer suddenly freeze completelly and the display shows some weird vertical lines, i can´t do nothing but pressing and hold the power button to shut down.

trying to debugg de problem,

FIRST
i notest that it happens when the computer get hotter,
so i played a dvd to reproduce the problem and after some seconds the problem appears
after this the computer get more freezy and even freeze when booting

SECOND
i tryed to start the computer without the battery and for my surprise the computer didn´t power on
so here´s is where i thought, is an electrical problem

THIRD
i start the computer using a good conditions battery, i start several applications including, itunes, activity monitor, and i played a dvd movie
everything works nice however after an hour, preciselly when i remove the dvd disc the computer freeze again with same vertical lines in the screen.

so i want to be sure of what the problem is, i haven´t tryed the PMU reset thing yet, i will today, but besides that it looks is the AC power card isn´t?
i would like to be sure first to get a new one since in this days i´m very miserable, no money and no computer
please
any help will be appreciated

Augusto from chile

ok, i work today in this machine doing dvd studio pro, and other applications at the same time, the computer was fairly hot but it worked fine until let say four hours, until i did something like open another application or something can´t recall what i did anyway
i tried the PMU reset thing after this freeze, boot and i played an audio CD,
to try works fine, after some minutes i opened dvd studio pro and freeze again although this time it freeze whitout the vartical bar lines just freeze including the audio (as a loop)
then i reboot (with the cd inside) and freeze again in the booting but with the old vertical lines again

i feel that is an electrical problem, but i´m not sure
please hint hints!

I highly doubt this is a hardware problem. This problems seems like it's a gradual one, and I assume it doesn't happen when you move the powerbook? Because if it happens when you move the powerbook, the video cable to the logic board is probably the problem. It COULD be the Logic Board or LCD, and if the symptoms are gradual, then it's probably temperature related.

Do me a favour:

Run the Apple Hardware Test that came with the computer and see what it tells you and let me know what it says.

ok,
finally i run the Apple H. test
everything passed
( the computer is formated i'm only using the os x, 10.4.11 )

- the computer doesn't freeze when the computer is move
(when the computer freeze nothing responds, therefore i doubt is some cable)

actually now i can make the computer freeze,
playing an hd movie (hdd file) and force it to play as fast FPS as the computer can,
then always freeze

it looks when high process is happening the computer freeze,
mmm,
i'm using the temperature monitor software and everything looks under the normal
even when it freeze
however since the image freeze i can't see if the temperature software has increase its numbers.

i'm lost,

could the AC power card haves something to do with this, considering that
the computer doesn't start without the battery?

because if is not this, is the logic board right?, some hardware power unit inside the logic board? that obviously i can't fix..

please help!