grey screen on startup on ppc g4 quicksilver

good day all,

i had ppc g4 quicksilver 933 , and it just sit on my room, never use.

last week i turn it on, and everything went well, but last night, when i turn it on, it gave me grey screen without apple logo.

this morning i re-seat RAM and VGA agp card, turn it on, rist it gave me grey screen and after i restart with the little button below the power button,

it gave me a message "memory test failure, please contact apple technician".

i isntalled 3 of 512k of RAM, and it detect only 512 k of RAM. what is going on?

please i need help, thanks.