PC turns on for 30 seconds than turns off repeatedly

Feb 3, 2019
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I am building a new PC and for some reason, it doesn't work. If I connect the four pin ATX power connector, the PC turns on for 30 seconds than turns off repeatedly, If I don't(because i am not sure if its necessary), the PC stays on but it doesn't connect to any monitors. I replaced every piece (except my new graphics card, the tower, and the ram stick.) and it still doesn't work. I tried different monitors and HDMI/VGA. I also checked for overheating. can anyone help?

motherboard: ASRock AB350M Socket AM4 AMD B350 DDR4 SATA3&USB3.0 M.2 MicroATX
hard drive: Western Digital Caviar Blue 320 GB Bulk/OEM Hard Drive 3.5 Inch, 8 MB Cache, 7200 RPM SATA II WD3200AAJS
PSU: APEVIA ATX-VS450W Venus 450W ATX Power Supply with Auto-Thermally Controlled 120mm Fan, 115/230V Switch,
CPU: AMD Ryzen 3 2200G Processor with Radeon Vega 8 Graphics
RAM: Patriot Memory Signature Line DDR4 4GB (1x4GB) UDIMM Frequency: 2400MHz (PC4-19200) 1.2 Volt - PSD44G240082

thanks in advance