I finally decided to upgrade the RAM in my '07 Macbook from 1 GB to 2 GB. I take out both of the old DIMMs, put in the new ones, and the sleep light comes on, but no actual booting. I power it off again, take out one of the new DIMMs, put in one of the old ones, and it boots just fine with one of the old, one of the new. I go to System Profiler, and it reports 1.5 GB. I power it off again, and trade out one new DIMM for the other. It boots, and reports 1.5 GB again. I power off, take out the old DIMM again, put in the other new one, so it has both new 1 GB sticks, and it refuses to boot once again. I've checked, and both DIMMs are seated properly. With it booting and reporting both of DIMMs when paired with an old one, I'd think that they both are good. What could I have done wrong?