My computer is a memory whore.

[Certaken]

My computer has a mega problem with always running out of memory. I can't run Minecraft and Action! (my game recorder) at the same time because my computer is always using up 5 to 6 GB of its 8 GB of RAM. I've been giving Minecraft either 0.5 GB of RAM or 1.5 GB of RAM because of it. I don't have any clue why my computer is doing this. It never did this before when I had Windows 8/8.1; it's only been doing this since I downgraded to Windows 7 again. The real problem is that I have 16 GB of RAM that I bought, but the timing is off and it doesn't work with my computer. How can I fix this?

 

[Tradesman1]

What mobo, CPU and model of DRAM?