Prime95 assigns a calculation to your computer. It knows the proper solution. If your computer returns the wrong solution, the test fails.
Prime95 failure indicates your system is unstable, but does not resolve the source of the instability. It could be CPU, memory or motherboard instability.
I suggest first using Memtest86 to test your memory for stability at a given memory frequency. Adjust timings/Vdimm as necessary for several error-free passes. Save some time by using several passes Test#5 (block moves), since that test is usually the most critical.
Then move on to Prime95 to test for CPU stability, adjusting Vcore as necessary.
Hope this helps!