Got a stick of 512MB, which should be PC2100, in today. Stuck it in, PC won't post, nothing, monitor won't come on, etc etc. Tried pulling out my current stick and just using the 512MB, in both slots, and it wouldn't work. So I'm assuming the stick is just deffective. Then I notice it says 512MB DDR PC266 on it, I ordered PC2100... did they just send me the wrong module, or is the 266 just some different number? It still fit in my ram slot though.