hmm very odd, have tried mixing the sticks around...i.e if you have a stick of crucial and your new stick and a generic stick, try it with just one of teh sticks or the generic and new, or crucial and new etc. Try other dimms you have in the been using in particular slot that the new stick resides in. Either your having memoyr confliction problems (rare nowadsy but it happens), dead DIMM slot, or the new stick you got is dead. try just your one stick in a known working slot by itself if it doens't work it's most likely a DOA (dead on arrival) stick of ram and you need to RMA it (return mail address....call the place you got it they should replace it for free)....
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