Well it looks the drivers were installed, but a yellow exclamation mark could mean more than that. Check to see if the exclamation marks have a description of the problem, if any are there. Can you get an internet connection on any other device or PC?
How did you determine that the new LAN drivers are installed? The OP didn't reinstall the OS. He said that the LAN is enabled in the BIOS, but there's nothing about the installation of LAN drivers for the new motherboard and I'm sure that the old ones won't work.