I have an optiplex 745 with 2GB of memory.I wanted to upgrade, so I used my service tag to find the correct memory for my machine and then I ordered the dell recommended memory for my machine.I got the memory but the machine won’t boot with it installed. I call tech support and they claim that they memory won’t work on my machine. I check dell.com, kingston, corsair and they all list 2GB 800Mhz memory for the optiplex 745 but when I read the docs for the 745 (every form factor) it says that it doesn’t support 2GB 800Mhz memory. Its weird dell recommends it for my machine and other companies all suggest 2GB 800Mhz for my machine. Anyone get this type of memory to work on this machine? The lady from dell recommended I exchange the 2GB for 2x1GB sticks instead, I only have 32-bit xp so I will only see 3-4GB of memory at the most.I have the latest bios 2.6.3 installed.

Source: Optiplex 745 supported memory options – General Hardware – Desktop – Dell Community