faulty ram slot

Hey all. I was tweaking around with the computer last night, since i wanted to get more RAM for my PC, and wanted to see what type of ram I already had. I took a piece out, made some photos of it and put it back in (slot 3). However, the PC didn't see that RAM stick anymore. It told me I only...

My second ram slot doesn't seem to work. When I have a RAM stick in it it starts, boots Windows up, then when I start to play a game, or do something, I get a bsod, or just a blank deep blue screen or it just freezes entirely. After that I have to manually power it down, by pressing the power...