Question My pc not working

Feb 20, 2021
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Hi i bought

Processor - i5 9400f ,
Motherboard - b365M ds3h rv1.0
Coasair ram - 16x2 2666

These thing new rest all old

Smps 550 volt

I install processor and processor fan in motherboard then add ram and only add atx, atx 12 volt and short via power pin its boot only 1st then i close assembled then after that its not start no response at all i try all way , add ssd and all other parts too but nothing happen , any one tell me how i troubleshoot what issue in this i cant figure out which part not work , these part totally new and still not work so please help me out with your suggestion..
Help me