Motherboard User Guide/Manual:
https://www.gigabyte.com/us/Motherboard/H310M-S2H-20-rev-10/support#support-manual
However, that link is for Rev 1.0 - your motherboard may be a different version or different in some other manual.
You must verify that the User Guide/Manual is indeed a match to your motherboard. Read all of the print on the motherboard itself.
Tutorials can be helpful in many ways but sometimes there are errors, details that are overlooked, etc.
It is time for a "do-over". Find the manual. Read it carefully while looking at your current installation and configuration, Do not immediately start changing things. Also read the installation Guide/Manual for all installed components.
If you find something that is not as expected or as it should be then make some notes accordingly. Make a list of questions and concerns.
For example, if there is only one stick of RAM which slot does the motherboard's User Guide say you should use. Did you use that slot?
Again read everything, including fine print and footnotes. Go to the manufacturer's websites for current information. Likely there are some updates regarding changes, documentation errors, etc..
Frankly, you should probably take the build all apart with the possible exception of pulling the CPU. Still you need to read and ensure that the CPU is fully supported by the motherboard.
And overall, what PSU is being used: make, model, wattage, age, condition? If the PSU is not up to the task of supporting the build's power demands - all will be for nought.
Do not do any overclocking etc. Objective is to get the build up and running smoothly. Performance can be tweaked later on once you have some assurance that all of the components are compatible and functioning.