had 8 GB RAM, now I have only 6

so yeah, this morning my monitor just stopped showing anything, then I try to turn off my pc via ALT-F4 and it did not respond, so I had to restart it with the button. Then the motherboard starts beeping, and the guide says that it indicates that there's not a memory installed in the motherboard. Checked all the memories, worked with 3 of them, except the one that was in the first slot. They have almost a year and now I'm afraid that the other 3 have a short life left too :(.

Btw, my memories are like (this)[http://ecx.images-amazon.com/images/I/41mjkv1f0HL.jpg] and I don't know if they are good or not because I didn't built the PC.