From what I have read about MSI Mobo Trouble Code "AB" just means you are in BIOS Setup.
Did you have a previous older AMD processor in your MSI Power Gaming Titanium Mobo?
If so did you check with MSI Support QVL List for RAM to see if it is compatible with the new 5800X Processor?
You can also check at AMD RAM List for the 3000-5000 Series processors from here: https://www.amd.com/en/products/ryzen-compatible-memory-ryzen-3000-to-5000-series-processor
Sounds like BIOS found some hardware that needs to be configured in BIOS or is not working correctly that was having problems during POST when BIOS was checking the Mobo and attached hardware before loading Windows.
You did the first step by installing the latest BIOS Version which is what is mentioned in the MSI Mobo CPU SUPPORT LIST.
Make sure you have all the CPU or Aux Power cables connected to your Motherboard. it is normally a 4 or 6 or 8 Pin cable connection. The computer won't boot up if that is not connected to the Mobo.
This will be a pain but to eliminate and narrow the problem down you need to disconnect all hardware from the Mobo and just leave the PSU and CPU on with all Mobo cables connected.
Turn on power with the side panel off and see what Digital Trouble code shows up. With just the CPU installed you should get a DRAM Digital trouble code since no RAM is installed.
Install one stick of RAM and now it should show Digital Trouble Code of no GPU installed and so forth.
If you install one stick of RAM and it goes to Digital Trouble Code 'AB" again then you probably found the problem. I would try and borrow another RAM stick that is compatible with your 5000 series processor and Mobo and see if the AB code changes to something else.
This way you can narrow down whether the problem is with the CPU or DRAM or GPU or something else.
