I just updated the RAM on my MacBook from 1GB to 4GB.
When I close it up, put the battery back in and start it the sleep lamp only blinks.
When I remove the battery and ram/L bracket and only use the power cable the computer works fine. Shows that 4GB ram in "about this computer". So there is something with the ram/L bracket..
Yes, I've really pushed the memory in really hard! My mac: 2 GHz Intel Core 2 Duo