My private server has 2x1gb Ram working with a 64bit Debian and an Q6600 Intel.
This runs 2 virtual mashines on it each one recives 512mb RAM.
Which you can immagine is a bit tight for the hole system.

Now i got 2x2gb ram from a friend. I'm not sure if thery are clocking at the same speed, but i'm sure my power adaptor is not on his limit and can handle that.
So there are 2 ram sockets left at the mainboard. I shuted down the system and build in the 4 gigs and looked what happen.
After pressing the start button, everything gets noisy as known BUT the screen shows nothing, not even the bios stuff it usally does.

Why isn't the system booting? I can immagine that it does not direkt link between booting debian and the bios not showing a thing. Or is it Grub? I mounted the system disk, and i can see it, switch folders write stuff with "vim" it does not seems like there is a problem.