Win10 Update 1803 Causes Dell Pc To Be Unbootable

Hi,

I have an older Dell Dimension 9200 64bit intel processor, 4GB RAM, running 32bit windows 10 release 1703. I was able to get as high as release 1709 but the automatic update to 1803 caused the PC to be in a non-bootable state.
I used a cloned version of my installation to get back to a working machine which got me back to release 1703.
I called MS support and they really weren't able to help me at all. The computer is on a small office network. The network domain contains 4 computers.
I am basically stuck at 1703, but Windows is always trying to update to 1803. It must be either some driver or program that is not supported with the upgrade, but I have no way of knowing what or how to diagnose it.
Oh, one more thing. I used a MS compatibility check utility off of MS website, and it told me that I have a version of Avira Antivirus installed on the computer which is not supported, but it is not installed! I used IOBit Uninstaller to check if it exists, and it does not.
So, does anyone know if I'm stuck or is there anything that I can do to further diagnose?

Thanks, in advance.