Reddit reviews Intel Celeron G4900 Desktop Processor 2 Core 3.1GHz LGA1151 300 Series 54W BX80684G4900

Here you go:

Intel Celeron G4900 Desktop Processor 2 Core 3.1GHz LGA1151 300 Series 54W BX80684G4900 https://www.amazon.com/dp/B07938X457/ref=cm_sw_r_cp_api_RL0ZBbZ8PEK1T

Please do, if you can get a borrowed Intel 8th Gen processor that would be great, if not you can buy a processor like this one:
https://www.amazon.com/Intel-Celeron-Desktop-Processor-BX80684G4900/dp/B07938X457/ref=mp_s_a_1_fkmrnull_1?crid=17NJPMHZU5UZM&keywords=intel+g4900&qid=1555181543&s=gateway&sprefix=intel+g4&sr=8-1-fkmrnull

Okay, so you just have the motherboard and CPU, RAM, and NVME drive. No video and still A0 error code I am assuming. There are a few possibilities here. Since this is a brand new build, its possible the BIOS is not up to date. While the motherboard should support the 9900k out of the box, additional 9th gen CPU support was added in BIOS versions F8 - F10.

There are inexpensive CPUs you could pick up to test your system with as well as update the BIOS: https://www.amazon.com/Intel-Celeron-Desktop-Processor-BX80684G4900/dp/B07938X457/

Here is your motherboard manual: https://download.gigabyte.com/FileList/Manual/mb_manual_z390-aorus-master_1001_190219_e.pdf

While you are trying to get this working, install RAM in 1st and 3rd slot only (2 sticks), and leave the video card out. Try booting into BIOS like that. Make sure the only things plugged into PC are monitor, keyboard, and mouse, and network. If that does not get you into the BIOS, I would suggest getting that cheap CPU and trying to see if you can use it to get into and update BIOS. Do NOT install Windows if cheap CPU works, or your license will be used up.

Sorry I don't mean to sound rude or mean but you bought a PC with an i5-8600k in a H310 motherboard and 4gb of Ram?

That is a very atypical combination.

Did you put the build together?

If so, I would suggest, at the very least, getting another 4gb of ram. If all you do is browse the web, the i5-8600k is not required.

Given that you already have an H310 board, I would suggest for you to get something like this:

https://www.amazon.com/dp/B07938X457/?tag=pcpapi-20

It costs less than $50 US.

The i5 8600k is worth around $250 new so you could probably sell it easily for $150. This would give you enough money to buy the extra ram, the processor I linked above and leave you with extra cash.

As to the temp question, It's probably because you did not put your Cooler on properly. (Did you forget to put the paste on?). Or maybe you did not tighten it or forgot to take off the plastic covering the cooler?

edit: just thought of this, perhaps the software you are using to report temperature is not doing so correctly. Maybe try re-installing the software or try a different one.

In addition, you can try to go into BIOS (usually something like hitting delete key before you boot into windows to see what CPU temp is being reported there.

Intel Celeron G4900 Desktop Processor 2 Core 3.1GHz LGA1151 300 Series 54W BX80684G4900 https://www.amazon.com/dp/B07938X457/ref=cm_sw_r_cp_apa_i_4F0wDb8JQ7R0N

Just get this used. Looks like there's one for $32 shipped.