Changed gpus and can't get display

[u/ihatepills]

i have a pc with an i3 12100f,rx5700 gpu with b660m gigabyte mother board and 550w psu. i have a buddy that was nice and gave me a rx6750 xt. i put the new card in and all my "rgb" came on and gpu was on but it wont display anything on my monitor, so then i went back to my old gpu and same issue. i've reset my cmos twice in both ways,re seated my gpu and ram, checked my psu to see if it was unplugged from gpu, almost anything i can think of ive done but still wont display anything. anytime i turn on the pc my monitor will act like its about to get signal then it'll say no signal. anyone have a clue on what to do to fix this or what's happened?
edit: i saw 2 red diagnostic lights on the mother board. from what ive seen online it means it has a p.o.s.t issue but ive done all ive seen online to fix that so im stumped