I recently got 21.5" iMac i5 (mid 2010) with 2x2 gigs of RAM installed. I decided to order more RAM online and bought from Crucial another 2x2 gigs (I made sure via their guide that I'm am buying the right RAM). Today I received the RAM and after installing them the iMac started to crash. It didn't crash on normal use but if I tried to make a disk check or do a memtest, it crashed (the screen went darker and there appeared a black box saying that I need to reboot). I did a disk check via the OS X DVD and everything was fine. I guess this means I have bad RAM or what? I took the new RAM away and everything seems to be fine, but I'm a little scared that even with the old RAM this thing might crash. I did install the RAM with care and read the instructions thoroughly. I guess one possibility is that one of the RAMs might have not been pushed back fully. Any suggestions or words of comfort?