Hello everyone. My friend and I just tried to upgrade the Ram on his 13" 2011 cMPB. Upon replacing the modules (they are compatible, 1333 mHz DDR3 from Crucial), when powering on, the system boots three times. The screen stays black. When we put in the old sticks, everything works fine. We were careful to de-static before working - but you never know. Is this a common issue? What do?