First of all, SpeedStep and Turbo Boost options (in BIOS) should be set to 'Enabled' - they're part of Intel's dynamic frequency scaling technologies, which enable Intel CPUs running at different speeds depending on various factors like workload, power, current, thermal limits etc.
Also turn off Hyper-V virtualization support, if it's enabled. Read this to learn more about how Hyper-V might influence processor speed readings on OS level.
This message was posted on behalf of Intel Corporation
Let’s try to narrow down the issue. Make sure you are using the latest BIOS version 2.0 of the motherboard Asrock H170 Pro4 then, check if memories are running at 2133MHz at 1.2V in the BIOS.
If problem continues, please run Intel® Processor Diagnostic Tool and Intel® System Support Utility. Post the results. I will be glad to help you.
Intel® System Support Utility
Intel® Processor Diagnostic Tool