For the issue with your case fans, do you have them connected to the SYS_FAN header on your motherboard? It appears you have 5 of these headers on the B550 board. You can use an adapter like this: PWM Fan Splitter if you want as it can help with cable management.
Once you have all the fans connected to this they should start spinning, the RGB part of the fans will need to be connected an ARGB controller. Which I cannot confirm if it comes with one or not, if it did, it would be in the back of the case behind the motherboard.
As for the PC not displaying on your monitor, I am assuming you tested this with the GPU since your CPU does not have integrated graphics. If the GPU is not outputting anything to the display, is the PC powering on and staying on? Do you happen to see any POST LEDs on the motherboard?
Let us know and we can assist you from there. If you would like to post some pictures of the build so we can see how everything is connected then that will help as well.
Have you tried the steps in our help article?
These should give you a good starting point for a checklist on things working. If you find one of these that doesn't work, let us know!
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