check to make sure your board supports that configuration. it would be weird that a board that takes that kind of processor wouldnt, but you never know. if it only accepts 128's in each slot, you never know what it will do. also, are they two sticks the same ? as far as speed ? (pc-133?) might try a bios flash, or running a memory tester such as docmem to see if somethings wrong (just because its working fine doesnt mean a stick couldnt be bad)