I recently doubled from 512mb to 1GB ram on my 1.25ghz, 15" powerbook by adding 512MB of some Japanese brand of memory called Century (?). Since then, OS X has frozen a couple times, often when the laptop is in sleep mode, it seems to go off eventually. Powering on the notebook sometimes requires several presses. Can this all be blamed on the RAM? I also have an old battery and am running out of hard disk space.