Elfen said:

Most of the time it is the RAM, like in 95% of the cases. But sometimes the 74XXX's chips to either side of the RAM can be bad in 4.95% of the time and in .05% a solder joint or trace goes bad. So check the RAM first, then the 74XXX's chps and finally the solder joints with a multimeter.

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i finished replacing the ram. (16ea)

i found that this computer  booting nomally except the screen.

just screen is not nomall.

screen was not changed, still has vertical lines.

i cant hear bong sound because sound was too low (soft?).

i guess this is not about ram problem.

do you have any idea? please tell me more