Hey guys, I recently sought to upgrade my late 2008 2.1 GHz Intel Core Duo Macbook from 1 GB of memory to 4 GB. I'm using 2 new 2GB RAM chips from Best Buy (PNY DDR2). Installed them...Macbook wont boot up (light turns on, black screen, sound doesn't occur/nothing happens). However, keeping one of the old 512 MB ram chips in and one of the new 2 GB ram chips in will work fine with total memory equalling 2.5 GB and the computer is quite faster...just having the two new ones in wont work. But, I know this Macbook is capable of 4GB total. I did a little research and found other people having similar problems with this issue, but really didn't find any definitive answer. Should I return the RAM and try a different brand? Any solutions? Also, for the time being, if I keep one of the new 2 GB PNY ram chips in along with one of the old 512 MB chips, should this cause my macbook any problems with things like crashes, updates, firmware, etc? (mismatched ram chips). Thanks!