What is most likely causing my pc not to post, or show bios?

We need your whole pc specs.

Your CPU isnt supported by that motherboard without a bios update, this is the 3rd one today, you need a sky lake CPU to upgrade the bios or a 200 series motherboard.

See here: http://www.asrock.com/mb/Intel/B150M-HDV/?cat=Download&os=BIOS
and here: http://www.asrock.com/mb/Intel/B150M-HDV/?cat=CPU

You need to have version P7.00 bios on there by the way before that CPU will work in that board.

The only way to update the bios is to get an older cpu that is supported by the current bios and update the motherboard with the old cpu in it. After it has been updated the i5 7600 will work.

It will be up to you. If you need the PC then go to PC shop ask for help. If you can wait, return it and buy the new MB.

I have been experiencing a similar situation with a custom build, not knowing the details of your situation, it's probably not the same issue, but this is a sure-fire troubleshooting start-point. I'll get to my quick analysis and potential solution now, then explain my situation briefly at the end.

Try powering off the system, pulling a stick of RAM out, and reseating it. Modern versions of Windows cache information about the hardware installed and during boot check driver versions and various other information that makes custom builds possible. The simple act of reseating RAM will force the system to, in a sense, re-calibrate itself. Even if you don't suspect a problem with the RAM, it is one of the easiest things to swap in a build, and should be the start to any troubleshooting.

In my personal experience, there is either a problem with my motherboard, power supply, or a flaw in Windows 10 which causes a similar failed boot scenario. Sometimes the system will stall with power to the mouse(optical light, USB), but no response on keyboard(num-lock enabled, but no light, also USB), it just sits, stagnant, fans running, disks spinning, but nothing happens. Other times, it will continuously reboot, but this is less common. It stalls for about 10 seconds, then restarts. The only solution is to pop a stick of ram and reseat it.

I tried simpler solutions, unplugging nonessential i/o devices, dropping to 1 of 3 monitors, removing the graphics card entirely and using just one monitor, nothing ever works to boot the system other than reseating the RAM. I isolated it to the motherboard, power supply, or windows for the following reasons:
Motherboard was open-box return to Microcenter. It might have been DOA, but the problem is intermittent.
Flaw in Windows 10 - Not so much a flaw, as a shortcoming. Microsoft did a great job with compatibility and native drivers on W10, but by nature, its universality and compatibility will always have some gaps or glitches. While I despise W10 for privacy reasons, it is fantastic for custom builds, but I'm pretty sure it is the root cause of my problem.
Power supply is the only remaining item from my continuously updating system which at one point sustained light smoke damage from a severe apartment fire. Thankfully I shut the door to my room upon evacuation, This act saved most everything. I now shut every door in my new apartment when I leave, and anytime I can, pay forward this piece of advice.

Sorry, I tend to ramble, but hopefully some bit of information was helpful either directly, or indirectly for the future.