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Your computer came with an Asus PTGD1-LA motherboard which is Socket 775 and is micro ATX form factor and supports PC3200 (400 MHz) /PC2700 (333 MHz) / PC2100 (266 MHz) DDR DIMM type. There are only two boards I found offered currently (in the US) which could simply be swapped without changing ram: The Intel BLKD915GAVL and the ASRock 775I65G R3.0
Not sure what you have available to you but with the specs shown above, you should be able to find something compatible.
Hope it helps