Can't enter BIOS B450 Steel Legend

TL; DR: Motherboard will not boot into BIOS

I have a B450 Steel Legend motherboard that will not enter BIOS. It starts up and goes immediately into a black screen. There is no splash screen and no beep from the chassis speaker. Here's my setup:

• Athlon 3000g
• ASRock Challenger 4Gb 5500XT Graphics Card
• Team T-FORCE VULCAN Z 16 GB (2 x 8 GB) DDR4-3200 CL16 Memory
• Apevia ATX-SP600W Power Supply
• DarkFlash 360mm AIO
• Crucial 256Gb SSD

So Far I have tried:

• Removing the GPU and using the integrated graphics
• spamming F2 on my keyboard during startup
• removing and moving around RAM sticks to different slots
• resetting CMOS by jumpering pins on motherboard
• removing CMOS battery
• disconnecting everything from motherboard except absolute essentials

... and it still doesn't work.

Sometimes, if I turn the computer off, plug in my boot drive, and turn it back on, it will boot into Windows and, as far as I can tell, works fine. When I start, the screen is black for a few seconds, then switches to the Windows splash screen. However, I can't boot into BIOS using Windows advances startup or ASRock's boot-into-BIOS utility.

I have discovered a method that works about half of the time. If I do a super-duper hard CMOS reset - remove the battery, disconnect the 24-pin power connector from the motherboard, unplug the power supply from the wall, hold the power button for 30 seconds, and let it sit overnight - the board will boot into BIOS. However, this only works once - on the next reboot, the previous behavior returns.

Oh, and I should mention, this is my second board. I RMA'd the board last month for this problem, and ASRock sent me a new one. After only a few reboots, this new board started behaving exactly like the old one.

At his point, I'm open to any suggestions. Thanks!

ThreeDee wrote: try a different monitor .. or if your monitor has different connectors .. try HDMI instead of DP or vice-versa.

Well I'll be damned ... Plugging it into a different port on my monitor didn't fix all of the problems, but it did get me to a point where I could boot into the BIOS reliably.

So, while putting my machine back together, I found where my boot problems started. Whenever I enabled the XMP settings for the RAM, the machine would start boot-looping. When I set the speed back to standard (2400), it would boot fine. The manual says the max speed for my configuration is 2666, so I set the RAM to that, and everything is all right. Strange that XMP at 3200 would stop working, as it's been set at that for months with no problems, but since it seems to be working fine now, I'll stop complaining

Looks like I'm back in business. Thanks again for the assist!