I added ram to my Advent 3117 desktop (put in an extra 2 gb). When I tried to switch the pc back on, the monitor was not turning on (but the pc itself was fine. There is also a clicking sound coming from my speakers as soon as I put the power back on (even before switching the actual pc itself on). I have tried putting the old ram back in without the new one with exactly the same outcome. I was told by 'Crucial' that the ram was compatible, but I may not have grounded myself well enough when going into the pc's insides. I also had to apply A LOT of pressure when inserting the ram into their slots - the computer is 8 years old and the slots had never been used before so were quite tough to use (they nonetheless clicked in no problem and were definitely inserted properly).
Check your video card and make sure it is plugged in tight. You may have bumped it when you installed the memory. If you had to put excessive force to install the memory you may have cracked the motherboard.