On a fresh install of Windows 10 pro 64-bit on Lenovo ThinkCentre M720s, model SEAG00, type 10SU.   Device manager shows several devices for which Windows can't find drivers, one of which is the Ethernet Controller.  Network and sharing shows 'no connection to network', and 'change adapter settings' shows no adapters.  RJ45 port shows solid red led (upper left) and flashing amber led (upper right).  Downloaded what drivers were available on Lenovo support site, but all attempts to update the driver are unsuccessful.  Diagnostics Evolution shows there is a problem with the device configuration - check device manager.

Where can I find drivers to manually install the 'ethernet controller' device?

Hello steveharke,

Welcome to Lenovo Community

I'm sorry to hear about the issues you're experiencing with your Ethernet Controller. You can find the necessary drivers on the Lenovo Support website.
Here's how you can do it:
Go to the Lenovo Support website here.
Enter your Lenovo ThinkCentre M720s model number in the search bar.
Click on "Drivers & Software" on the left side of the page.
Under the "Networking: LAN (Ethernet)" category, you should find the Ethernet Controller driver. Download and install it.
If you're still having trouble, you might want to try using the Lenovo Vantage app. It can help you update your drivers and diagnose any issues with your system. You can download it from the Windows app Store here.
I hope this helps! If you have any more questions or need further assistance, feel free to ask.

Best regards,
Lorenzo_Lenovo

Hi steveharke,

How's your M720s Ethernet controller doing now?
We hope everything is working fine.
Any update would be much appreciated.

Regards, 
Lorenzo_Lenovo

Thanks for sharing the steps to have this fix but just wondering if it was previously working so likely new changes has been the trigger. 
Instead of a free installation, the original Factory preloads (via DDRS) are advised that would restore both working Windows 10 Pro build version along with the certified drivers.

Regards, 
Lorenzo_Lenovo

This unit appeared to be a re-refurb - no existing OS installed, so I can't tell if it had been working before or not. 

Please try to manually update all packages offered from the support site to apply with the appropriate Windows version. 
If same case after, then consider reporting this to tech support.

Regards, 
Lorenzo_Lenovo

Hi,

I would also suggest that you use a different network when resetting device using DDRS with its context menu.

Regards, 
Lorenzo_Lenovo