I have an older HP pavilion 900mhz machine that only will allow 512 megs of ram because of the cpu limitations. The primary slot has one 256 stick (Kinsington KTH-PVL100/256 and the second slot has a 64 MB stick) and all works ok. I replaced the 64 with another 256 but the computer will not boot. If I go back to the 64 then all is well. Is it possible the new 256 is the incorrect frequency? How can I tell?