Question Ryzens + b350 prime plus

[jason991]

I just changed my Ryzen 3 1200 to Ryzen 7 2700. Then pc wouldnt boot anymore. I realized that my bios version was too old and thats the reason why it wouldnt work out. Then i changed back my old ryzen 3 1200 and surprised that it wouldnt work either anymore. Fans are spinning and RGB's are working in the motherboard but I get no signal on the screen.
I have resetted CMOS, tried with one ram stick etc. And im sure my GPU is fasten right.
Any ideas what should i do?

 

[Barty1884]

Just to be 100% sure, you've connected your display to the GPU and not the onboard HDMI etc, right?

 

[jason991]

I am 100% sure about that. It does not even beep once when I turn it on, it did before when pc was working.