[SOLVED] new build, gpu gives black screen(NOT no signal, 640*480 black screen) on monitor, keyboard and mouse work

Aug 10, 2020

I'm building this on the motherboard box for now and have hooked up the case power button to make it easier to troubleshoot.

Asrock b450m pro4, box says ryzen 3000 and 2000 supported.
Ryzen 7 2700
Inno3D 10606gb oc 16gb (1x16)
hyperx fury 3200 HX432C16FB3/16 in slot 2.
corsair cx550

all the fans spin up (including psu and gpu) initially monitor shows no signal. After a few seconds it changes to checking signal and shows an HDMI input, 640*480, blank screen. the keys on the keyboard work(caps, scroll lk lights), mouse lights up, f10 and enter reboots the system (is what it looks like). Gpu gets slightly hot, cpu is very cool. have tried various ram slots, cmos reset. have tried a different display (tv) and cable. no difference. Without any gpu plugged in, everything still turns on and spins, nothing on the display obviously but the keyboard and mouse light up still but unlike before they dont respond to clicks.
Sometimes, the gpu fans dont spin/stop spinning if i wait at the black screen for a while or reboot. Sometimes one fan stops the other runs.
Have checked the cables multiple times, reseated the CPU, no bent pins there. Reseated the Mobo, RAM is installed all the way in, I cannot find whats wrong.