iMac (mid-2010) RAM upgrade issue I recently upgraded an iMac to 16 GB of RAM using 1600 MHz clock speed sticks. It worked fine, but I came to find I was supposed to install 1333 MHz sticks instead. So I tried switching the current modules with the appropriate 1333 MHz memory modules and the computer won't boot up; the iMac would just beep until I unplugged the power.

I've tried various combinations with the 1333 MHz RAM and no luck getting it to boot. Is there a system preference that I have to reset in order for the computer to accept the RAM?
I managed to get the slower RAM to work by resetting the PRAM/NVRAM:
http://support.apple.com/kb/ht1379

Works like a charm now.