First time builder, PC stuck in a boot loop.

Components: Case-Cooler Master Box Q300L Mb-ASRock B450m Pro-F AM4 PSU-Seasonic Focus 450 Gold 450w (semi modular) Gfx-Gigabyte Radeon RX 570 4GB RAM-Ballistic Sport 16GB DDR4 CPU-AMD Ryzen 5 2400G HD-Seagate Barracuda 2TB SSD-Patriot Memory Burst 240GB

Will turn on for about 10 seconds, then turn off for about 2 seconds, then turn on for 10 seconds, etc. No POST. As far as I can tell everything seems to turn on.

I've tried troubleshooting through multiple YT videos and online how-tos, plus I double checked the manuals and all seems good to go. Reseated most things except CPU. Removed some and all of the RAM, too. Everything that should be plugged in is plugged.

I'm a complete noob when it comes to this stuff, but I'm also a broke and independent bitch so I thought I could do this with a help of a friend but they're stuck on the issue, too. Any help anyone can give me would be very much appreciated.