Since yesterday I'm having the EXACT samt problem. I have updated BIOS to the latest FW 3004 but it didnt solve anything.
I have
ASUS B450-E Gaming ATX
Corsair Vengeance RGB PRO 16GB (2x8GB) / 3200MHz
Ryzen 5 3600
Water cooling (deepcool castle 240 EX)
ASUS RTX 2070 Super
Everything worked great until I tried to start the computer yesterday...
After BIOS update I even pulled the cable and removed CMOS battery to resest the whole thing. Didnt help.