I see, I am the noob after all

GeForce GTX 580 1.5gbs

So what can I do??

http://www.tomshardware.co.uk/forum/306303-12-windows-64bit-shows-73gb-usable-memory-installed

That's an example of someone with similar issues to you, they resolved the issue by reseating the memory a few times. I would recommend you do the same if this has worked previously as its unlikely to be a issue with the OS unless you have been fiddling prior to this occurring.

I'd also recommend while you have it open you inspect to see why your fans are running faster. It maybe worthwhile investing in a air duster and cleaning out the fans and heatsinks and ensuring there is no obstructions to the fans cooling the PC.

Nvm me, check what others are telling you :)

Nobody ever stops being a noob when it comes to PC's as there is always something to learn no matter how much you may know .  A good memory, sound logic and a lot of patience are probably more important than knowledge in the long term lol.

thx for answering. The only thing left is to open my PC and see what the hell is going wrong D:

Open resource monitor and see whats going on with your memory...

Indeed, I did also read this can be the CPU not correctly aligned in the socket on the main board so that might be a good idea to remove the heat sink, reseat the CPU carefully (be gentle as if you bend the pins its bye bye motherboard) then clean off the old thermal paste and apply new and replace the heatsink.  If you haven't done any of this before then get a friend who has to help or take it to someone who does know what they're doing.  Nothing worse than butchering your own hardware by accident.

Try the memory suggestions first as its easy, harder to screw up and cheap to replace if memory is the issue.

Sometimes you can physically see the transistors that burned up on chips, but if you pull them out, replace them and it doesn't solve your problem. Good chance it is dead. Just find out which one is the bad one and replace it.