I have a dell optiplex 755 desktop it is installed 1 GB ram of DDR2 and I tried to upgrade the memory to 3 GB I installed another 2 GB in the other slot but while powering up the monitor is not getting signal and there is a beeping sound coming from the mother board when i tried to change the bios setup I found the memory channel mode is a single only and 1 GB and these setting can not be change>
please is there anyone can tell me how to install the 3 GB ram?
for more information the 2 GB stick is twinmos and the old 1 GB is samsung.
Bad DIMM slot on Motherboard
RAM speed/timing on the new memory stick won't work with that motherboard
Bad DIMM from manufacturer
Brand Incompatibility between RAM sticks from two manufacturers
Brand Incompatibility between new RAM stick and motherboard
My recommendations would be to remove the original memory stick and replacing it with the 2GB stick in the slot that the 1GB stick was installed. If it posts, it's either a dead port on the motherboard or the memory sticks aren't working together.
If it doesn't work with just the 2GB stick, try to install that in a different computer and see if it accepts that memory stick. If not (and it's compatible with that other PC) then it's a bad memory stick.
I have installed 4 GB in a 755 before but if it's one of the original models it may have issues. Crucial has a free utility that will scan your computer to tell you what is installed in your machine and let you know what size and speed of RAM you can use in that computer. I might run that utility to see what it advises you to install.