4k video editing ,preview standstill problem. ? Please Help.

Looking at the specs of those individual components, it looks like your system is just simply too weak to handle 4K material. Three things are deficient, in your case:

1) The CPU. It has only 4 cores and 8 threads, and it has a slow all-core Turbo speed as well. As such, it is slower than even a stock i7-4790K, let alone an overclocked one.

2) Only 16GB total system RAM. For 4K you need at least 32GB of system RAM (but 64GB or more is better).

3) The Quadro M2000 is functionally the equivalent of only a GeForce GTX 950. It is based on the previous-generation Maxwell architecture, with only 768 CUDA cores and a memory throughput outside of CUDA applications of only 106 GB/second. Those are practically the exact same specs as a GTX 950 (both of them based on a cut-down version of the GM206 GPU), with small differences in the GPU clock speeds.