Sounds like either you have the wrong memory modules or they are not properly seated in the slots.
Exactly which Macbook do you have and what RAM modules did you buy?
and then > MacBook: How to remove or install memory
For quality RAM upgrades,
Lastly, this is the Intel iMac section of the Apple Support Communities and the section for Macbooks and Macbook Pros is over at > Notebooks: Apple Support Communities
I spoke with an apple rep (1800myapple) last week to find out whether or not my machine was compatible with mountain lion and found out it is not. It is, however capable for install of lion, but only with a memory upgrade from 1gb to 2 gb. I then purchased from said rep two (2) 1gb memory chips. So, I doubt it's the wrong chip, and that it's an improper install. I did as instructed in the manual, there is only one way they will seat properly allowing proper reassembly. Again, I reinstalled the original memory chips and got the same result. A machine that has no start up chime that appears to be in sleep mode but wont wake up. I hope this is helpful.