Upgrade to 4.0 - Non GUI Enviroment

I'm hoping someone can help me with this.

First I am NOT running nopCommerce in a GUI environment.  I am running Server 2016 Core as a VM and have had it running for over a year under Nop 3.8 with no issues.  I have decided to go to Version 4.0

After a few failures I decided to go first to 3.9.   I ran the SQL Upgrade Script to 3.9, then copied all of the files for 3.9 over the top of the current 3.8.  I only did a quick check, but everything seemed to be working.  

I then ran the SQL Upgrade script to 4.0, and copied the files over the 3.9.  Now when I try to go to the site I get a 500 - Internal Server Error.

Anyone have any suggestions?

Turn off custom errors to see details -  https://www.nopcommerce.com/boards/t/27211/frequently-asked-questions.aspx#110220

You can also try to query the dbo.Log table

Thank you for the reply.  I check my web.config files to change custom errors, and didn't have the line <customErrors defaultRedirect=  in any of the web.config files that I looked at.  Also I am not finding the dbo.log file. :(

Any other ideas?

Since it is a VM I did set a checkpoint to 3.9.  I might just go to back to that version, but I'd really like to get 4.0 working if I can.

All of this is being done on a "Practice Machine", so I'm not down.  My live server is still running 3.8 so this isn't any type of emergency.

Well the Checkpoint back to 3.9 didn't work :(  Guess i will re-import and start again.

Currently i am getting the following error after attemting to upgrade to nopCommerce 4.0:
An Error occurred while starting the application
.NET Framework 4.7.2558.0 X86 v4.0.0.0  |  Microsoft.AspNetCore.Hosting Version 2.0.0-rtm-26452   | Microsoft Windows 10.0.14393

Here is what I have done:
I started again, and upgrade from 3.8 to 3.9.  
I did more testing, and I couldn't find anything not working.  
I upgraded the Database with the sql script file - No Errors.  
I then copied the 4.0 files over the top of the 3.9 files.

Since the directory structure is so different with 4.0 I tried copying the contents into the inetpub folder, and I tried ti copying the contents into the inetpub\wwwroot folder.  I'm pretty sure that the first was the Correct location, but it didn't make a difference.

What might I be missing?  Remember I am NOT running "Windows".  I am running MS Server 2016 Core, so a non graphical windows!

Thanks for any help you might be able to give.