Question Help! Gaming PC won't turn back on

[spookmama]

My son's new gaming PC (that he also uses daily for school work) was working great and today while he was in class, it just shut off and will not turn back on. Its a custom build that has been up and running beautifully for three months. When we try to turn it on now, the RGB lights and the fans in the case turn on for a split second and then nothing. It's like it starts the process of turning on but something is missing so it turns right back off? We tried removing the CPU and GPU and reinstalling with no change. The monitor registers being connected to a graphics card. Any suggestions of what to do from here? We are both pretty new to this! Thanks!!!

 

[spookmama]

Here's the build:

MSI VGA Graphic Cards RX 580 ARMOR 8G OC

TEAMGROUP Elite Plus DDR4 16GB Kit (2x8GB) 2400MHz PC4-19200 CL16 Unbuffered Non-ECC 1.2V U-DIMM 288 Pin PC Computer Desktop Memory Module Ram Upgrade - Gold & Black - TPD416G2400HC16DC01

Samsung SSD 860 EVO 1TB 2.5 Inch SATA III Internal SSD (MZ-76E1T0B/AM)

MSI MPG B550 Gaming Carbon WiFi Gaming Motherboard (AMD AM4, DDR4, PCIe 4.0, SATA 6Gb/s, Dual M.2, USB 3.2 Gen 2, HDMI/DP, Wi-Fi 6 AX, ATX, AMD Ryzen 5000 Series Processors)

Apevia ATX-PR800W Prestige 800W 80+ Gold Certified, RoHS Compliance, Active PFC ATX Gaming Power Supply

MUSETEX ATX Mid-Tower PC Gaming Case 2× USB 3.0 & 6× ARGB Fans, Computer PC Chassis with Remote Control, Tempered Glass Cooling System/Airflow/Cable Management（T400-MS6）

AMD Ryzen 7 3700X 8-Core, 16-Thread Unlocked Desktop Processor with Wraith Prism LED Cooler