Dell Xps 600 Memory

A few months ago I was having major issues with my computer where I would get blue screens. I was told that my RAM could be to blame, and when I removed two of my memory sticks (my PC came with four 512MB samsung cards), all my blue screen problems went away. So I've been running on 1GB of memory, which is what I want to fix. Just today I tried to put those two sticks back in and my computer would not start. When I turned on the power, the computer beeped a few times, but nothing happened.

So my question is should I try to replace these chips because they are bad, or could it still be something with my computer?

Thanks