I have an Optiplex 390 MT. It shipped with the 2GB of the following RAM :

Dell part number 1N7HK

DUAL IN-LINE MEMORY MODULE, 2G, 1333, 128X64, 8, 240, 1RX8

And the following motherboard:  MIH61R

The computer will not accept any new RAM. After I add RAM all I get is a blank screen with a flashing cursor.

I have tried both PC3-10600 and PC3-12800.  I tried Dell Certified - HYNIX 4GB 2Rx8 PC3-10600U DDR3 DESKTOP MEMORY HMT351S6AFR8C-H9 and that didn't work either.

I have the latest BIOS A11