Samsung 850 evo 500gb i take it this ssd is due for the bin,did a fresh install of windows and it took forever to do and windows is running very slow. 4690k 16gb ddr3
Oooof, 16MB/s write, thats not good! How long have you had it for? Tried the Samsung SSD toolbox? It may suggest something.
What does the health report say? Before you throw it away, try using secure erase program to write flash all default state value. I can't remember which is the flash default state, is it all 1's?