thanks for trying to help guys!
It's working now, all I did was this:
I have 4 slots for RAM, 2 and 2 are together
For better cooling I had 256RAMs on 1st and 3rd slot
The thing is, that you can't have 2 different size of RAM on a pair of slots (1st and 2nd or 3rd and 4th)
I had to move one 256 so that both 256 were on one pair of slots (1st and 2nd) and put 512 into 3rd slot
for better understanding:
these are slots: 1 2 -- 3 4
I had: 256 empty -- 256 empty
It didn't work like this: 256 512 -- 256 empty
Or like this: 256 empty -- 256 512
But it works like this: 256 256 -- 512 empty
I hope that I can help with people with RAM problems