I want to buy a new pc and i want the cpu: (INTEL CORE I7-5820K) and rams: (KINGSTON HX430C15PB2K4/16 HYPERX PREDATOR 16GB) but rams are 3000mhz and the cpu supports 2133MHz what that means? There is no cpu that supports more than 2133mhz
The DIMMs themselves are rated for 2400MT/s and should work fine at 2400MT/s as-sold. While the CPU is not officially spec'd at 2400MT/s, people have been overclocking the memory to that sort of level for quite a while. There would be no point in memory module manufacturer making DIMMs spec'd at over 3000MT/s if no CPU's memory controller could be overclocked that high.
Check the Bios version you have on the motherboard. My Gigabyte UD4 originally came with only the first release version F5. I've had to install an updated bios to F9 to address memory issues. The most recent bios update is F13a.