Seemingly random BSOD's.

I did it once in a computer science class before, don't remember what it was though, it's been 5 years.
Also, it's what the instructions tell me to do, so I'm clueless.

Edit: Just got kicked from Arma 2, with corrupted memory error.
First time I have that so it's either a big coincidence or it pushes it to the RAM area for the most likely cause of the BSODs.

Edit 2: Too tired so I'm going to bed for at least 8 hours, I'll let Memtest run all the time.
If it keeps going like this I think it's going to give errors.

Well, somehow last time I did the memtest it did a full pass without errors, this time it threw errors all around (5000+) within 10 minutes, 3 times straight.

I suspected the cheaper brand of RAM being the culprit (which unfortunately is half of my RAM), and I'm pretty sure was right, I started memtest, waited 15 minutes without errors.
I went to bed, woke up with 19 passes, no errors.
So it seems like the new cheaper brand stick died in half a year.
From 8 GB of RAM to 4 GB, I'm going to see if it bothers me too much or if I don't notice it before I re-order (a better brand now) another stick of RAM.

Thanks for the help and the suggestions, I'm going to wait about a week before I mark this as solved if it's fine for you guys, in the meantime I already +repped you guys for the help and time so far. :)

Thanks for the hint, I'll keep that in mind. :)